Make accountDB optional.

[Foxcapades]

Problem

Container core validates that accountdb is configured and reachable regardless of whether it is actually being used.

Right now for a service to use auth at all, container core requires accountdb to be configured. For new services, or services that have been updated to use oauth, accountdb is not necessary, however must still be set up for a service to be usable.

Proposal

Alter the requirements of the auth filter through some means to allow for services to exclusively use oauth without needing account db to be configured.

Perhaps as an interim fix while accountdb's direct use by services is being pruned from our services, container core can check for the accountdb and/or oauth environment variables before deciding whether accountdb should be mandatory?

For example, if a service requests auth be enabled, however only the oauth env vars are present, log a message indicating that legacy auth is disabled and continue without accountdb.