Require any event where a GitLab team member will be speaking to have at least two speakers from an underrepresented group

Why is this change being made?

Events where GitLab team members are speaking, need to be in line with GitLab's values. This MR documents the event requirements for organizers to create a diverse and inclusive speakers schedule, and have speakers from underrepresented groups. This is a new policy and required for team members to be able to speak at the event when accepted or invited.

This MR also documents the process for speakers

• Requirements prior to the submission
• Event speakers lineup review when a talk gets accepted

@lmcnally1 @melsmo @johncoghlan @nwoods1 Please review.

Note: This MR is a change affecting all team members and will need an announcement in #whats-happening-at-gitlab in Slack.

FYI @akramer @gitlab-de

Additional context

• CFP issue timeline, retrospective, actions
• Slack thread (internal)

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.
• 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
• 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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