Allow unmanaged attributes in KC for local dev

[eleftherias]

Summary

Update Keycloak config in local docker image to allow for unmanaged attributes. Without this the attributes gh_id and gh_login weren't getting mapped into the token correctly, which was causing problems when looking up the user.

Fixes #4084

note: It is intentional that there's a JSON string in the YAML file. It would be nice if they offered a better configuration option, but this is the way to do it for now.

Change Type

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• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

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Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 54.406% (+0.004%) from 54.402%
when pulling 790929f on eleftherias:4084-local-kc
into 2646d77 on stacklok:main.