Previously the initializer always loaded the `application_settings`
table in the initializer, even for Rake tasks (e.g. `rake
db:setup). This was done because the usage ping worker needed to load
the UUID of theins instance from the database to calculate the usage
ping schedule. However, cron schedules are only needed by Sidekiq, so we
can defer the calculation of this value in the Sidekiq initializer.

When loading application settings from the database, this should make it
possible for us to raise errors when the connection is not present since
this appears to be the only setting that is actually needed at init
time.

This came out of a discussion in
https://gitlab.com/gitlab-org/gitlab/issues/205640.