feat(Cloud Databases): Update Database Password Complexity Validation

[alexhemard]

This reverts commit 768de21.

Original PR: #5701

IBM Cloud Databases will begin enforcing password complexity validation for database users created using the IBM Cloud console, CLI, API and Terraform. Database user passwords will be required to be a minimum of 15 characters, contain at least one letter and number and a mix of uppercase and lowercase letters.

This PR will enforce the new password complexity requirements for the ibm_database resource

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Relates OR Closes #0000

Output from acceptance testing:

make testacc TESTARGS='-run=TestAccIBMDatabaseInstance'

--- PASS: TestAccIBMDatabaseInstanceEDBReadReplicaPromotion (2582.95s)
--- PASS: TestAccIBMDatabaseInstanceElasticsearchImport (362.50s)
--- PASS: TestAccIBMDatabaseInstanceEtcdImport (564.16s)
--- PASS: TestAccIBMDatabaseInstanceMongodbBasic (1137.46s)
--- PASS: TestAccIBMDatabaseInstanceMongodbImport (413.52s)
--- PASS: TestAccIBMDatabaseInstanceMySQLReadReplicaPromotion (1232.17s)
--- PASS: TestAccIBMDatabaseInstancePostgresBasic (1247.36s)
--- PASS: TestAccIBMDatabaseInstancePostgresGroup (2089.95s)
--- PASS: TestAccIBMDatabaseInstancePostgresImport (629.16s)
--- PASS: TestAccIBMDatabaseInstancePostgresPITR (1444.50s)
--- PASS: TestAccIBMDatabaseInstancePostgresReadReplicaPromotion (1473.86s)
--- PASS: TestAccIBMDatabaseInstanceRabbitmqImport (465.61s)
--- PASS: TestAccIBMDatabaseInstanceRedisImport (478.76s)
--- PASS: TestAccIBMDatabaseInstance_ElasticsearchPlatinum_Group (1334.44s)
--- PASS: TestAccIBMDatabaseInstance_ElasticsearchPlatinum_Node (1820.28s)
--- PASS: TestAccIBMDatabaseInstance_Elasticsearch_Basic (722.37s)
--- PASS: TestAccIBMDatabaseInstance_Elasticsearch_Node (1829.77s)
--- PASS: TestAccIBMDatabaseInstance_Etcd_Basic (2921.06s)
--- PASS: TestAccIBMDatabaseInstance_Rabbitmq_Basic (933.21s)
--- PASS: TestAccIBMDatabaseInstance_Redis_Basic (1010.33s)

$ go test github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/database 
 
ok  	github.com/IBM-Cloud/terraform-provider-ibm/ibm/service/database	0.923s

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