feat: DMS replication endpoint MySQL settings block

[mdjward]

Description

This adds the MySQL settings block to the existing DMS replication endpoint resource.

I'm aware that #23506 would supercede this (I personally agree, the proposed design is better), so recognise that this contribution may be short-lived.

Relations

Closes #20396

References

https://docs.aws.amazon.com/cli/latest/reference/dms/create-endpoint.html
https://docs.aws.amazon.com/dms/latest/APIReference/API_MySQLSettings.html
https://docs.aws.amazon.com/sdk-for-go/api/service/databasemigrationservice/#MySQLSettings

Output from Acceptance Testing

% make testacc TESTS=TestAccXXX PKG=ec2

...

[github-actions]

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[github-actions]

Welcome @mdjward 👋

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