Adds Enablement Specialty to MOps Job Family

Why is this change being made?

This change is being made to add an Enablement specialty to the Marketing Operations job family. This aligns with our plan to add Enablement as a pillar of the Marketing Operations team and outlines the Enablement scope of work, which is distinct from the roles currently listed in the job family.

This MR also makes a couple minor changes:

1. Eliminates the justification section under the Principal Marketing Operations Manager, since it was the same justification as the Staff level.
2. Changes the Independent Contributor heading to Individual Contributor

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.

---