Add primary keys to all tables

[timdreier]

Topic and Scope

The PR adds primary keys to all tables to fix #2531 and #1984.

Concerns/issues

Shouldn't have any impact.

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