Upgrade to Vue3

[christianlupus]

Topic and Scope

This is a technical update of teh Vue system to the new version 3. Some changes are needed as previously used Components were Vue2-only.

Concerns/issues

Is the PR potentially cause any issues that might be of interest? Any other issues to be tought of?

It is just a WIP state at the moment.

Formal requirements

There are some formal requirements that should be satisfied. Please mark those by checking the corresponding box.

• I did check that the app can still be opened and does not throw any browser logs
• I created tests for newly added PHP code (check this if no PHP changes were made)
• I updated the OpenAPI specs and added an entry to the API changelog (check if API was not modified)
• I notified the matrix channel if I introduced an API change