Test additional file patterns with action serializers

[OdenTakashi]

Summary

This PR demonstrates that action-specific serializers can be annotated with the existing additional_file_patterns option.

For example, serializers named like this:

app/serializers/test_default_index_serializer.rb
app/serializers/test_default_show_serializer.rb

can be picked up with:

additional_file_patterns:
  - "app/serializers/%MODEL_NAME%_*_serializer.rb"

This allows serializers such as TestDefaultIndexSerializer and TestDefaultShowSerializer to receive the schema annotation for TestDefault.

This is a reference PR to demonstrate that action-specific serializers can be annotated with the existing additional_file_patterns option.

[OdenTakashi]

Sorry, I opened this PR against the upstream repository by mistake.

This was intended as a reference/demo PR on my fork while discussing #329, so I’m going to close it for now.