A copy of getsentry/sentry#22657 with fixes included.
That said this one is a bit different. We used to use the extra option `no-merge` when publishing to keep the release branches and also keep master on nightly versions. If we want to keep this, we need to add per-project overrides to getsentry/publish which would increase complexity at this early stage for this fringe case. Instead, I opted to follow what getsentry/sentry does: merge but then immediately after that update the version.
This change allows one to override any Sentry service image, mostly for testing purposes. It also removes the SENTRY_VERSION variable as docker-compose makes it very hard to cascade default values for these. Next step is to have integration tests in getsentry/snuba and getsentry/relay (and possibly for getsentry/symbolicator) for getsentry/onpremise using this PR.
Also related: #596.
