chore(auth): Backport Gen2 config to Gen1 JSON for older authenticator versions

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:

Description of changes:

• When using Gen2 config we will rebuild the Gen1 JSON blob for use by older versions of Authenticator that haven't been updated to use the AuthConfiguration directly.

How did you test these changes?
(Please add a line here how the changes were tested)

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)

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

[tylerjroach]

Gen2 will be a minor version bump. We don't claim to support older versions of authenticator with a minor version bump on Amplify (see https://github.com/aws-amplify/amplify-ui-android?tab=readme-ov-file#supported-versions).

This is a decent bit of extra code to maintain, and very temporary in its usage. Thoughts on not providing this mechanism at all?

[tylerjroach]

After discussing, looks like we should support this.