Update steps for MVP noms and selection

Why is this change being made?

• Follow-up from 14.9 Release Post Retro

MVP selection is sub-optimal

Current process has the RPM soliciting MVPs on the 12th (optionally sooner) and choosing an MVP on the 15th.

Proposal:

• The new automatic Release Post job will create the MVP issue on the 1st
• MVP issue can be modified to include a mention to @gl-product and @community-team requesting nominations
• Opening steps will be updated to encourage RPM to share a link in #release-post, #community-relations, #mr-coaching and #core Slack channels
• On the the 12th, instead of soliciting MVPs, the RPM will encourage votes on the noms
• On the 15th, the RPM chooses an MVP based on votes

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
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this change to the correct DRI(s)
  • 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 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.

---