feat(rds): Support SQL Server for RDS proxy

[daschaa]

Closes #22164

As stated in the issue the iam auth has a third option with the support for sql server. I did not add it in this pull request, because replacing the boolean property iamAuth with a string property would lead to breaking changes.
We should open up another issue for this and fix this separately.

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[daschaa]

Exemption Request: I think this needs no README entry :)

[corymhall]

🚀

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

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