Migrates the current data in one keyserver table to two. It works a bit unusually but the general gist is:
- Copy the data from keyservers to keyserver_synced_data
- Fetch the data in the migrations (db ops will merge the data from keyserver and keyserver_synced_data and so return the correct KeyserverInfo)
- Save the data in the migration (db ops will now split the data correctly into two tables)
Also adds the non-synced keyservers table to backup blocklist.
Depends on https://phab.comm.dev/D11481