Move incubation engineering roles under a more consistent job family structure

Why is this change being made?

Migrate the incubation engineer and management roles into the appropriate structure.

See also https://gitlab.com/gitlab-org/incubation-engineering/meta/-/issues/23.

I've based my changes on the job family template 1.

I labeled Incubation Engineer as such leaving off the "Intermediate" modifier in most cases. When doing so I preferred the prefix form "Intermediate Incubation Engineer" since that's consistent with frontend/backend engineer job family pages rather than following the guideline of using "Incubation Engineer (Intermediate)".

What changes are being made?

• Create a job family page for Incubation under Engineering with the following structure:
  • Roles > Engineering Roles > Incubation Roles
    • Engineer
    • Management
      • VP
• Create a job family page for Incubation Engineer under Incubation with the following structure:
  • Roles > Engineering Roles > Incubation Roles > Incubation Engineer Roles
    • Incubation Engineer
    • Senior Incubation Engineer
    • Staff Incubation Engineer
• Create a job family page for Incubation Engineering Leadership under Incubation with the following structure:
  • Roles > Engineering Roles > Incubation Roles > Incubation Engineering Leadership
    • Director, Incubation Engineering
    • VP of Incubation Engineering
• Move the existing VP of Incubation Engineering page to VP under the Incubation Engineering Leadership job family mostly untouched.
  • Roles > Engineering Roles > Incubation Roles > Incubation Engineering Leadership > VP of Incubation Engineering
• Add @bmarnane as a CODEOWNER for the sites/uncategorized/source/job-families/engineering/incubation/ directory.
• Marked VP as an acronym for helper functions which were previously causing "Vp" to be rendered as the link text for VP roles under engineering and more in the handbook.
• Added table of contents to all incubation job family pages.

Author Checklist

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• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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