WIP: feat: Allow migrations to run on first release when no in-cluster database is enabled.

Exploring if we can solve #50 (comment 296353354) in-chart.

The idea is to allow both initializeCommand and migrateCommand to run on first release (in that order), and do it as a pre-install hook if no in-cluster postgres is enabled.

The pre-install part only works if we can assume the database is live pre-install. This certainly is true for externally configured databases, but I'm not sure if it is true for ones provisioned via crossplane. This needs further testing.