Improve "Is this the Red Team?"

Why is this change being made?

This MR iterates on our process for dealing with the question "Is this the Red Team?". We have a good working process already in place as it related to ongoing stealth operations. However, there was nothing specifically documented to say how we answer this question when a stealth operation is not in progress.

This MR does the following:

• Condenses the "Is the the Red Team?" section to link to our rules of engagement for more specifics
• Adds a new method to contact the Red Team outside of official operations
• Some basic editing for clarity

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added, and the content is SAFE
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (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 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
  • The when to get approval handbook section explains the workflow in more detail
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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