Remove call to update_db.pl from Dockerfiles

[sekjal]

Describe the issue
The last layer of the Docker deployments has a call to both installer/update_db.pl AND plackup. While this makes sense in some ways (verify the DB and the container are in sync), it has a couple problems:

1. When deploying multiple replicas, there is a race condition between the replicas to do a database upgrade, which may result in crashes/failures if creating/updating tables.
2. Not every instance of the container needs to be running the web server; sometimes you just want to do the initial setup, or run the crons.
3. in the Alpine image, there appears to be an intermittent issue about SSL not being supported; the unit tests addressed this by giving more time for the container to start up before, but the underlying cause seems tied to update_db.pl

Proposed solution
Remove the update_db.pl call but keep plackup. This means you'll get a running instance of Libki Server on 'up', but you may need to run some setup (create_instance, create_user, update_db, etc) either manually in the container or programmatically through docker-compose and one-time containers

[kylemhall]

This seems like a reasonable approach. Should Libki could have a "login to upgrade" style screen ala Koha, a notification screen if the database version doesn't match the. code version, or just "do nothing" and if there are errors, there are errors? I see some merit to each approach.