Add support for multiple SASL/SCRAM associations for MSK clusters

[mmehrten]

Description

Many MSK users want to create SASL/SCRAM secrets in multiple modules and associate them with the cluster. Today, the aws_msk_scram_secret_association resource is effectively a singleton and blocks this type of use case.

This PR adds logic to manage configured state for multiple aws_msk_scram_secret_association objects separately.

Relations

Closes #16791

Output from Acceptance Testing

TF_ACC=1 go1.23.2 test ./internal/service/kafka/... -v -count 1 -parallel 20 -run='TestAccKafkaScramSecretAssociation_update'  -timeout 360m
=== RUN   TestAccKafkaScramSecretAssociation_update
=== PAUSE TestAccKafkaScramSecretAssociation_update
=== RUN   TestAccKafkaScramSecretAssociation_update_multiple_associations
=== PAUSE TestAccKafkaScramSecretAssociation_update_multiple_associations
=== CONT  TestAccKafkaScramSecretAssociation_update
=== CONT  TestAccKafkaScramSecretAssociation_update_multiple_associations
--- PASS: TestAccKafkaScramSecretAssociation_update_multiple_associations (2293.89s)
--- PASS: TestAccKafkaScramSecretAssociation_update (2297.66s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/kafka      2303.569s

[github-actions[bot]]

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