refactor: move Karma migration utilities to the migrate-karma-to-vitest directory

[alan-agius4]

The standalone migration is no longer used.

[gemini-code-assist]

Code Review

This pull request removes the remove-default-karma-config migration and its associated tests, while consolidating Karma configuration utilities. The review feedback highlights that several import paths in the migrate-karma-to-vitest migration were incorrectly updated to point to a parent directory instead of the local folder. Additionally, the generateDefaultKarmaConfig function should remain exported as it is still required by the unit tests.

[alan-agius4]

This PR was merged into the repository. The changes were merged into the following branches:

• main: 7c1eede

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