Merge upstream fixes on making listbyuser more efficient

Contains upstream (ETH Zurich) changes for:

• fixing the number of database queries when performing the listbyuesr API call.
• removing frontend docker-compose file, merging with backend (now we need to use --profile frontend)
  • both: https://gitlab.ethz.ch/vseth/sip-com-apps/community-solutions/-/merge_requests/418
• remove wiki transfer and legacy solution functionality (this was already removed in our repo)
  • https://gitlab.ethz.ch/vseth/sip-com-apps/community-solutions/-/merge_requests/419

A manual merge resolution performed where necessary to accommodate for repo-local modifications such as payment/wiki features already being removed in our version.