docker/collabora: Switch to gthread worker type
The current eventlet worker type has no limit on number of database
connections it will create. This causes the database to run out
connections and return "FATAL: sorry, too many clients already"
errors.
The gthread worker will only serve limited amount of requests at a time thus will no longer exhaust the connections. It can also make use of persistent database connections and HTTP connection reuse.
Upstream switched to gthread worker as of LAVA 2024.03.