Update the forum workflow community handbook

Why is this change being made?

This MR revises the community forum workflow handbook page:

• Remove the outdated issue boards and bots section
• Add a Users section explaining the CoC and flag posts action we discussed in Slack (internal)
• Clean up the page and remove personal metions. Instead, linking to as the SSoT for admins: https://forum.gitlab.com/about
• Fix the mermaid render issue - labels with special characters need double quotes around them.

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files. (this requirement has been removed pending identification of a new DRI for the handbook)