EM Growth is replaced with a Fullstack Manager specialty

Why is this change being made?

The Engineering Manager Growth job family is no longer used

Existing EMs for Growth were:

• first moved to Backend EMs (there was talk of a Growth/Fullstack speciality being created)
• later moved to Fullstack Managers (ogininally proposed as a combined manager, when this was changed to Fullstack it aligned better with Growth EMs actual role)

I think this file just got left behind. MR removes it and the job family entry, and adds Growth specialty to Fullstack Manager.

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
• Assign this change to the correct 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 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 relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files. (this requirement has been removed pending identification of a new DRI for the handbook)

Approvals (as this introduces a specialty)

https://about.gitlab.com/handbook/hiring/job-families/#approval-flow

• Manager @whaber
• Executive @edjdev
• Recruiting @Kellymurdock
• CEO @sid
  • while CEO reviews, mention @gl-total-rewards

Note there are already four specialties for Growth in BambooHR (one for each group) - this MR merely adds Growth as a specialty to the job family.

Merged with 1 follow up issue to discuss engineering manager naming convention #11757 (closed) - this MR retains the status quo.