Run database initialization after startup

[benno-mueller-saxess]

I want to run some database initialization script after the server has startet successfull (Log: "LOG: Datenbanksystem ist bereit, um Verbindungen anzunehmen"). I'm using currently image postgres:12.18

How can I do this with an Dockerfile?

[tianon]

See #173, #821, #191, #929 for some other issues that have some good thoughts / suggestions (one of/many of which this is probably a solid duplicate of).