Zoom Rooms Plugin

[pferreir]

This is the third instalment of https://github.com/indico/indico/pull/6475. See also https://github.com/indico/indico-plugins/pull/236

Changes:

• RAVEM - move to SUI, in line with changes in core

• Zoom Rooms - new plugin and tests, as well as some documentation (README)

  TODO:

• [x] Replace https://link/to/docs with the true URL, once there is one. Or even better, add a plugin setting to set the URL.
• [x] Fix failing unit test and add unit tests to CI
• [x] Add some more docstrings