Add support to wait for database to be available before running migrate

[hectcastro]

When using the update script, check to ensure the database is available before attempting to execute migrate.

[rbreslow]

I'd consider the seeing what the approach taken with wait-for-postgres.sh would look like. Maybe we could add it in a update.d directory?

It doesn't particularly spark joy, but especially if we'd ever like to use the 3.0 Compose file format, we'll need to adopt something like this eventually.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[pomadchin]

Replaved via #29