Fix migration health check endpoint

What does this MR do and why?

Map migrations check to the custom all-migrations health check implemented for Rails 7.2

Background

The health_check gem does not work with Rails 7.2 because ActiveRecord::Migration.check_pending! was removed upstream. To fix this, we added a custom check in !204700 (merged). This check is run in the standard / full checks.

We also support running a specific check via the /health_check endpoint. Users can provide a specific check (or an underscore-delimited list of checks) by providing it in the path. For example: /health_check/migrations or /health_check/cache.

This MR fixes this endpoint so that migrations is mapped to our custom check.

References

Related to #584785 (closed)

How to set up and validate locally

Visit http://gdk.test:3000/health_check/migrations. It should return success if your migrations are up-to-date.

Note: You need to restart GDK for the initializer changes to take effect

MR acceptance checklist

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