This fixes a bug in which sidekiq histograms contain invalid labels.

See https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/7729
for more details.

Fix for https://gitlab.com/gitlab-org/gitlab-ce/issues/66319.

This adds diirect monitoring for sidekiq metrics. This is done via
sidekiq middleware and a sampler to pull from sidekiqs api.