feat: add plugin for DSQL auth tokens

[danielfrankcom]

Summary

Adds a new dsql plugin which creates authentication tokens for Amazon Aurora DSQL.

Description

Changes include the added dsql plugin, which is an extension of the existing IamAuthConnectionPlugin with a custom token generator. Both new files are unit tested.

A new dependency was added which customers will also need if using the plugin. Requirements will be documented in an upcoming change.

Credit to @karenc-bq for the initial plugin implementation.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[danielfrankcom]

Latest change is a simple rebase to update the branch with the latest main.

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Update to e07c358 addresses a few issues:

• Avoid wildcard imports as requested
• Add support for extracting region from connection string for DSQL
• Fix test issue caused by rebase

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Update to a7378b3 changes the dsql plugin name to iamDsql.

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Update to bb1f7c5 uses a static mock instead of a test-only constructor.

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Update to a1c6593 fixes some formatting issues which were flagged by the GitHub actions.

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Update to 7c9c3fc removes a unit test dependency on the system AWS credentials provider.

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Update to 3e6bd2a addresses a comment by adding a user-facing warning message if the DSQL SDK dependency is missing.

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Update to 4dfd2a0 addresses an offline comment from @deepakscomk about a possible error for subsequent calls to generateAuthenticationToken with different credentialsProvider or region.

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Update to 8c3d0a7 performs a rebase to pull in a fix from main for a javadoc error.