Configure proper priority for route tables

[hanwen-cluster]

#2855 made the pcluster route table/metric number larger (meaning lower priority). Thereafter, some unwanted default rules on AL2023 ec2-net-utils took priority and failed test_multiple_nics integration test on AL2023. Then, #2857 made the number too small, interfering route table configurations from IMDS on AL2.

Therefore, this commit tries to imitate the priority prior to these two PRs. This is not the cleanest fix, because it is staying in the lucky priority range instead of fully resolving the issue (i.e. prevent IMDS and ec2-net-utils from configuring the route tables). However, this commit is the least breaking change. So I propose to go with this commit.

Metric number range before the two PRs
Network card (0,0): 1000
Network card (0,1): 1000 (which was causing conflicts and the reason for all these PRs)
Network card (n,1): 100n (for p5, which has 32 network card, it will be 1000-10031)

Metric number range after the first PR:
Network card (0,0): 1000000
Network card (0,1): 1000001 (conflict fixed :) )
Network card (n,1): 1000001+n*1000 (for p5, it will be 1000000-1031001)

Metric number range after the second PR:
Network card (0,0): 10
Network card (0,1): 75
Network card (n,1): 0x(hexadecimal number)n01+10 (for p5, it will be 10-12555. The hexadecimal number was accidentally introduced because bash automatically interpret numbers start with "00" as hexadecimal number)

Metric number range after this commit:
Network card (0,0): 1000
Network card (0,1): 1001
Network card (n,1): n01+1000 (for p5, it will be 1000-4101)

Tests

• multi-nic tests on RHEL8, Rocky8, AL2, AL2023, Ubuntu20, Ubuntu22 have passed

Checklist

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• Check if documentation is impacted by this change.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.63%. Comparing base (10395d1) to head (ac3e225).
Report is 34 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2858      +/-   ##
===========================================
- Coverage    76.67%   76.63%   -0.04%     
===========================================
  Files           22       22              
  Lines         2242     2243       +1     
===========================================
  Hits          1719     1719              
- Misses         523      524       +1     

Flag	Coverage Δ
unittests	76.63% <ø> (-0.04%)	⬇️

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