Unable to sync multiple geopackages from a single MM project

Nobody has claimed this yet.

Right now, syncing multiple geopackages from a single MM project on a single computer does not work:
- if there's one config file with multiple connections (to the same MM project), these connections use the same working project directory (in `$TEMP/dbsync`) - and that causes issues, because each connection should have its independent working directory
- even if there are multiple db-sync daemons running, each with a separate config file, this is still not going to work because of the working project directory collision as above. There are two ways to avoid working directory collisions in this case:
1. run db-sync in docker containers (each container has its own temporary directory); or
2. set a different temporary dir (using env variable) for each db-sync run

Both of these cases should ideally work without any fiddling needed... Probably we could just fix the local project directory naming so that they are more unique (e.g. include gpkg name, db schema name?)

No files or tests are named. Start by locating where db-sync creates the local project directory under $TEMP/dbsync and reproduce two connections targeting one MM project; done means multiple geopackages can sync independently without Docker containers or separate temporary-directory environment settings.

Written by the indexing model from the issue text.