Update doxygen documentation generation process

[jcfr]

There are few aspects to consider:

• Automatic trigger of doxygen documentation generation when
  • Slicer master branch is updated
  • Slicer pull request is created or updated
  • Slicer release is created
• Ensure documentation is up-to-date

To ensure documentation is up-to-date, we could simplify the current approach by:

• Updating CI associated with preview.apidocs.slicer.org and apidocs.slicer.org by switching to GitHub action
• Setting up a scheduled workflow like what we do for Slicer/.github/workflows/update-slicer-certificate-bundle.yml

This would allow to have up-to-date documentation for master main branch of Slicer.

Once that is addressed, we could then move forward with:

• doxygen documentation preview for pull request (similarly to what we have for readthedocs)
• automatic release of doxygen documentation

Hints

• Revisit use of https://github.com/Slicer/github-circleci-trigger and instead look into event dispatching
  • https://blog.marcnuri.com/triggering-github-actions-across-different-repositories
• Transition CI of this repo from CircleCI to GitHub action
• Switch to use of peaceiris/actions-gh-pages and remove use of gh-pages-squash.sh and trigger-travis-squash.sh. For example, see Slicer/slicer.org/.github/workflows/build-website.yml#L41-L52