Create local development setup

Noting a TODO: "make tests" is taking a snapshot, maybe we can use DDEV snapshots for this instead.

Noting another TODO: The /opt/project mount might not be needed with this setup, since our contrib project is available at /var/www/html and we could presumably use that as our composer symlink.

@star-szr: I would suggest dropping the "make snapshot" from the "make tests" target in this context- I believe that is cruft from the example I referred you to, which was a project where the tests themselves would restore this snapshot to reset the state. In this case I think that's overkill, and only slows the tests process down.