[fix](be) Default to the Default chain when S3 role_arn is set without provider_type

[CalvinKirs]

closed #60501

One-line summary
On the BE side, setting AWS_ROLE_ARN no longer implicitly forces cred_provider_type to INSTANCE_PROFILE; if AWS_CREDENTIALS_PROVIDER_TYPE is not explicitly provided, it now defaults to the Default chain.

Behavior change

• Before: AWS_ROLE_ARN only -> INSTANCE_PROFILE
• After: AWS_ROLE_ARN only -> DEFAULT (Default chain)
• Explicit config still wins: AWS_CREDENTIALS_PROVIDER_TYPE=WEB_IDENTITY -> WEB_IDENTITY

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[Thearas]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[CalvinKirs]

run buildall

[doris-robot]

TPC-H: Total hot run time: 28615 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpch-tools
Tpch sf100 test result on commit 7daab178d8b0021219b868b17e63badd190495a1, data reload: false

------ Round 1 ----------------------------------
============================================
q1	17627	4455	4270	4270
q2	q3	10643	760	531	531
q4	4682	395	258	258
q5	7573	1233	1005	1005
q6	174	179	149	149
q7	776	834	697	697
q8	9324	1451	1287	1287
q9	4808	4667	4674	4667
q10	6760	1865	1616	1616
q11	461	254	242	242
q12	706	563	468	468
q13	17767	4242	3416	3416
q14	228	222	212	212
q15	921	803	788	788
q16	718	714	673	673
q17	705	847	426	426
q18	6101	5388	5277	5277
q19	1264	978	609	609
q20	507	491	386	386
q21	4665	1832	1387	1387
q22	340	282	251	251
Total cold run time: 96750 ms
Total hot run time: 28615 ms

----- Round 2, with runtime_filter_mode=off -----
============================================
q1	4416	4315	4334	4315
q2	q3	1776	2163	1724	1724
q4	868	1175	784	784
q5	4025	4286	4317	4286
q6	178	170	141	141
q7	1724	1591	1486	1486
q8	2401	2647	2510	2510
q9	7418	7446	7439	7439
q10	2607	2823	2438	2438
q11	527	446	416	416
q12	497	585	447	447
q13	3991	4439	3600	3600
q14	275	351	315	315
q15	849	788	797	788
q16	732	760	734	734
q17	1174	1633	1336	1336
q18	7072	6807	6566	6566
q19	874	945	969	945
q20	2100	2146	2011	2011
q21	3954	3536	3343	3343
q22	474	446	410	410
Total cold run time: 47932 ms
Total hot run time: 46034 ms

[doris-robot]

TPC-DS: Total hot run time: 184396 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpcds-tools
TPC-DS sf100 test result on commit 7daab178d8b0021219b868b17e63badd190495a1, data reload: false

query5	5240	637	516	516
query6	335	215	203	203
query7	4211	458	261	261
query8	343	254	238	238
query9	8764	2759	2745	2745
query10	563	364	329	329
query11	17032	16896	16603	16603
query12	189	124	122	122
query13	1257	433	332	332
query14	6800	3139	2987	2987
query14_1	2800	2792	2823	2792
query15	205	195	176	176
query16	989	469	462	462
query17	1064	742	611	611
query18	2713	443	342	342
query19	218	207	185	185
query20	139	127	129	127
query21	225	146	119	119
query22	5406	5618	5721	5618
query23	17612	17066	16971	16971
query23_1	17000	17048	17050	17048
query24	7559	1667	1312	1312
query24_1	1310	1303	1300	1300
query25	642	530	453	453
query26	1289	274	165	165
query27	2942	551	305	305
query28	4891	1910	1926	1910
query29	924	673	565	565
query30	321	275	228	228
query31	930	760	695	695
query32	81	74	69	69
query33	550	377	306	306
query34	1053	929	575	575
query35	618	658	583	583
query36	1074	1128	989	989
query37	132	95	84	84
query38	2942	2896	2883	2883
query39	883	884	830	830
query39_1	832	832	803	803
query40	223	149	133	133
query41	68	59	56	56
query42	108	105	104	104
query43	383	387	354	354
query44	
query45	197	187	179	179
query46	868	976	607	607
query47	2134	2107	2039	2039
query48	298	302	227	227
query49	618	456	393	393
query50	672	273	221	221
query51	4092	4046	4022	4022
query52	108	106	94	94
query53	289	334	301	301
query54	305	290	252	252
query55	89	78	78	78
query56	319	309	307	307
query57	1352	1327	1246	1246
query58	290	269	271	269
query59	2559	2680	2554	2554
query60	335	327	315	315
query61	145	142	146	142
query62	621	587	520	520
query63	308	276	275	275
query64	4789	1251	991	991
query65	
query66	1366	462	370	370
query67	16466	16421	16192	16192
query68	
query69	396	312	287	287
query70	980	994	966	966
query71	339	305	300	300
query72	2718	2656	2433	2433
query73	532	567	318	318
query74	9993	9883	9780	9780
query75	2832	2741	2436	2436
query76	2288	1032	679	679
query77	352	389	326	326
query78	11287	11493	10657	10657
query79	1245	774	599	599
query80	1370	625	511	511
query81	556	294	244	244
query82	978	147	121	121
query83	343	254	239	239
query84	253	120	95	95
query85	929	476	421	421
query86	431	312	290	290
query87	3126	3066	3026	3026
query88	3531	2652	2627	2627
query89	415	373	344	344
query90	1976	171	169	169
query91	165	160	138	138
query92	78	77	68	68
query93	995	836	496	496
query94	647	307	252	252
query95	586	394	319	319
query96	641	508	225	225
query97	2478	2451	2426	2426
query98	227	212	216	212
query99	1011	976	909	909
Total cold run time: 256276 ms
Total hot run time: 184396 ms

[hello-stephen]

BE UT Coverage Report

Increment line coverage 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	52.57% (19589/37263)
Line Coverage	36.16% (182685/505154)
Region Coverage	32.50% (141755/436151)
Branch Coverage	33.46% (61455/183650)

[hello-stephen]

BE Regression && UT Coverage Report

Increment line coverage 100% (0/0) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	57.38% (20941/36496)
Line Coverage	40.30% (202972/503654)
Region Coverage	36.98% (162847/440319)
Branch Coverage	37.65% (69362/184236)