Hard-code non-configurable sampler intervals
What does this MR do?
While these samplers had intervals in 1_settings.rb, those weren't
exposed anywhere else: in the gitlab.yml.example
file, in
gitlab.rb.template
in Omnibus, or in our Helm charts.
Based on that, it doesn't appear that we expected people to configure these intervals, so we should make the hard-coding explicit.
Closes #218309 (closed).