Publish a postgres enabled docker image

[data-sync-user]

Once we have a fully supported postgres backends for Tokenserver/Syncstorage we need to ship a docker image for both our own use (on GAR) and ideally provide the image on dockerhub for self hosters.

https://mozilla-hub.atlassian.net/browse/STOR-342 may end up accomplishing (or partly accomplishing) this task for its own usage.

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