GitLab::Sentry has a program_context method to determine whether a
Sentry exception occurred in Sidekiq or rails. Since we will need
similar functionality for distributed tracing, this change extracts the
program_context method into GitLab.process_name for more general
consumption.
The Correlation ID is taken or generated from received X-Request-ID.
Then it is being passed to all executed services (sidekiq workers
or gitaly calls).
The Correlation ID is logged in all structured logs as `correlation_id`.
This adds a method to track errors that can be recovered from in
sentry.
It is useful when debugging performance issues, or exceptions that are
hard to reproduce.
The initializers including this were doing so at the top level, so every object
loaded after them had a `current_application_settings` method. However, if
someone had rack-attack enabled (which was loaded before these initializers), it
would try to load the API, and fail, because `Gitlab::CurrentSettings` didn't
have that method.
To fix this:
1. Don't include `Gitlab::CurrentSettings` at the top level. We do not need
`Object.new.current_application_settings` to work.
2. Make `Gitlab::CurrentSettings` explicitly `extend self`, as we already use it
like that in several places.
3. Change the initializers to use that new form.
