Migrate Page editing controller endpoint to API

[guerler]

This PR further reduces the pages controller endpoint by migrating the edit endpoint to the api. The recently introduced client-side page creation form component has been generalized to also handle the edit form inputs.

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

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

[guerler]

Failing tests appear to be unrelated.

[guerler]

Thank you @mvdbeek!