Migrate display applications API to Fast API

[heisner-tillman]

This is a part of #10889.

Summary

• Add pydantic models
• Operations now return pydanctic models
• Removed the mapping to the legacy route and add FastAPI routes

How to test the changes?

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  You can find the interactive API documentation here: http://127.0.0.1:8080/api/docs#/display_applications

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[mvdbeek]

Nice work, thanks a lot!