WIP: Allow to cycle unicorn EE

What does this MR do?

This adds /-/reload that makes all workers of the given node to be restarted.

This allows us to ensure that we always start fresh.

This also includes various random fixes (that should rather be in separate MRs) related to gathering metrics:

• invalid worker name being used for RubySampler metrics when run from Puma,
• inconsistent naming of RubySampler metrics: today it is: sidekiq, 0..n, master,
• cleanup of prometheus metrics in dev/test environment,
• reduce default ruby sampler time to 5s,
• properly measure cpu_total_time, previously we would measure time spend in the thread, instead of the process,

Related to:

• https://gitlab.com/gitlab-org/gitlab-ce/issues/63570
• https://gitlab.com/gitlab-org/gitlab-ce/issues/63659

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team