Draft: Add Kubernetes Resource Limits

What does this MR do?

Added Kubernetes resource limits to gitlab-pages, gitlab-shell, and KAS. Added documentation to gitlab-pages, gitlab-shell, KAS, mailroom, toolbox, and registry for resource limits.

Related issues

Relates to issue

Author checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, follow the instructions in the "Reviewer Roulette" section of the Danger Bot MR comment, as per the Distribution experimental MR workflow

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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• [n/a] Tests added/updated
  • Testing not needed for the change made.
• [n/a] Integration tests added to GitLab QA
  • Not needed for the change made.
• [n/a] Equivalent MR/issue for omnibus-gitlab opened
  • Not relevant to the omnibus-gitlab setup
• [n/a] Equivalent MR/issue for Gitlab Operator project opened (see Operator documentation on impact of Charts changes)
  • Changes made not relevant to the gitlab operator project.
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.