Move conan check credentials to shared endpoints

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What does this MR do and why?

This mr moves the get credentials endpoint to the shared conan registry endpoints so it becomes available for v2. The change also adds a corresponding test for the conan v2 spec file.

References

• #333033 (closed)

How to set up and validate locally

Make sure you have a GitLab project that you can test with on your setup. Use the project id whenever you see <project_id> in the URLs below.

1. Switch the conan_package_revisions_support feature flag on.

   For GDK, open rails console (docs):

   gdk rails console

   Enable the feature flag:

   # Enable
   Feature.enable(:conan_package_revisions_support)
   
   # Verify
   Feature.enabled?(:conan_package_revisions_support)

2. Get Conan Authentication Token

   First, generate a base64-encoded Basic Auth token:

   # Replace with your username and PAT
   echo -n "USERNAME:glpat-YOUR-TOKEN"|base64

   Then use the output to get a Conan JWT token:

   curl --request GET \
   --url 'http://localhost:3000/api/v4/projects/<project_id>/packages/conan/v1/users/authenticate' \
   --header 'Authorization: Basic <YOUR-BASE64-TOKEN>'

3. Call the get_credentials endpoint

   curl --request GET \
   --url http://127.0.0.1:3000/api/v4/projects/<project_id>/packages/conan/v2/users/check_credentials \
   --header 'Authorization: Bearer <YOUR-CONAN-JWT-TOKEN>'

   that should return status 200 OK and body ok

/cc @oceane_scania