Documentation: Update link and information about Prometheus scraping TLS endpoint

What does this MR do?

This updates the webservice chart docs to provide a link to the Prometheus TLS scraping docs, and removes a now-inaccurate statement and link to the implementation issue for TLS-protected endpoints, as this is now implemented.

The current link is also confidential and will 404 for documentation users.

Related issues

• #3335+
• Add documentation and examples for Prometheus T... (!2671 - merged)

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, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• 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.