feat: Add support for Witness Region for Global Tables with MRSC

[shawnaws]

Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

No

Description

This adds support for leveraging a Witness Region in DynamoDB Global Tables with Mutli-Region Strong Consistency.

Relations

Closes #43612

References

Output from Acceptance Testing

% make testacc PKG=dynamodb TESTS=TestAccDynamoDBTable_Replica_MRSC_witness
make: Fixing source code with gofmt...
gofmt -s -w ./internal ./names ./.ci/providerlint/helper ./.ci/providerlint/main.go ./.ci/providerlint/passes
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
make: Building provider...
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.24.5 test ./internal/service/dynamodb/... -v -count 1 -parallel 20 -run='TestAccDynamoDBTable_Replica_MRSC_witness'  -timeout 360m -vet=off
2025/08/14 16:33:27 Creating Terraform AWS Provider (SDKv2-style)...
2025/08/14 16:33:27 Initializing Terraform AWS Provider (SDKv2-style)...
=== RUN   TestAccDynamoDBTable_Replica_MRSC_witness_doubleAddCMK
=== PAUSE TestAccDynamoDBTable_Replica_MRSC_witness_doubleAddCMK
=== RUN   TestAccDynamoDBTable_Replica_MRSC_witness_pitr
--- PASS: TestAccDynamoDBTable_Replica_MRSC_witness_pitr (216.84s)
=== RUN   TestAccDynamoDBTable_Replica_MRSC_witness_pitrKMS
=== PAUSE TestAccDynamoDBTable_Replica_MRSC_witness_pitrKMS
=== RUN   TestAccDynamoDBTable_Replica_MRSC_witness_tags_updateIsPropagated_oneOfTwo
--- PASS: TestAccDynamoDBTable_Replica_MRSC_witness_tags_updateIsPropagated_oneOfTwo (243.75s)
=== RUN   TestAccDynamoDBTable_Replica_MRSC_witness_tags_updateIsPropagated_twoOfTwo
^[[C--- PASS: TestAccDynamoDBTable_Replica_MRSC_witness_tags_updateIsPropagated_twoOfTwo (233.29s)
=== RUN   TestAccDynamoDBTable_Replica_MRSC_witness_tags_propagateToAddedReplica
--- PASS: TestAccDynamoDBTable_Replica_MRSC_witness_tags_propagateToAddedReplica (227.64s)
=== RUN   TestAccDynamoDBTable_Replica_MRSC_witness_tags_notPropagatedToAddedReplica
--- PASS: TestAccDynamoDBTable_Replica_MRSC_witness_tags_notPropagatedToAddedReplica (235.11s)
=== RUN   TestAccDynamoDBTable_Replica_MRSC_witness_tags_nonPropagatedTagsAreUnmanaged
--- PASS: TestAccDynamoDBTable_Replica_MRSC_witness_tags_nonPropagatedTagsAreUnmanaged (236.11s)
=== RUN   TestAccDynamoDBTable_Replica_MRSC_witness_tagsUpdate
--- PASS: TestAccDynamoDBTable_Replica_MRSC_witness_tagsUpdate (306.48s)
=== CONT  TestAccDynamoDBTable_Replica_MRSC_witness_doubleAddCMK
=== CONT  TestAccDynamoDBTable_Replica_MRSC_witness_pitrKMS
--- PASS: TestAccDynamoDBTable_Replica_MRSC_witness_pitrKMS (325.32s)
--- PASS: TestAccDynamoDBTable_Replica_MRSC_witness_doubleAddCMK (656.19s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/dynamodb   2363.769s
...

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