Add `EnsureJobChannel()` middleware method, intended for `compose/<id>`
endpoints. Its purpose is to ensure that the tenant channel set in
the request `echo.Context` matches the tenant channel associated with
the compose. In case of mismatch, `404` is returned.
Add `JobChannel()` method to the worker server implementation for
requesting channel associated with the job.
Extract the determination of tenant channel into a helper function.
This will simplify handler and middleware methods, which won't have
to implement the same logic by themselves.
Fix the multi-tenancy unit test to pass the appropriate context when
querying compose statuses, because the server that is being use has JWT
enabled and expects the tenant to be set in it.
