Add Wants=postgresql.service to Pulpcore service files

[ekohl]

Wants is a weak requirement, so the service won't fail it can't be started but systemd will at least try it. That should work with help when postgresql is local.

This was reported in theforeman/foreman_maintain#824. I don't know if this is sufficient or if foreman_maintain also needs to be smarter.

An open question: if we know PostgreSQL is managed, should we make it a hard Requires= instead?

[evgeni]

I'd not add a hard requires

[ekohl]

Reading this file I debated adding Redis as well, but wasn't quite sure about it.

[evgeni]

Makes sense (also to foreman and dynflow)

[sbernhard]

Make sense!

[ianballou]

A user reported on Discourse that this wasn't sufficient to stop the coredumps when stopping Pulpcore: https://community.theforeman.org/t/pulpcore-coredumps-during-stopping-services/36512/6

[ehelms]

We've identified this is still useful even if it does not address the particular problem discussed, which @evgeni has made headway with actually fixing through packaging.

[ekohl]

@ehelms while I was out, has additional testing been done on the stronger requirement, which was also suggested in https://community.theforeman.org/t/pulpcore-coredumps-during-stopping-services/36512/6?