Replace note on group multiselect

The multi-select note in the Setting Product Group for Team Members section of the handbook has been resolved by the note in Update Product Specialty.

Note: It is not currently possible to select multiple specialty field values for team members who are stable counterparts across many groups. We are working on a solution.

This MR replaces the text with:

• A team member who is a stable counterpart to the Access and Import groups in the Manage stage, and the Gitaly group in the Create stage would have specialty designations of Manage:Access, Manage:Import, and Create:Gitaly.

Why is this change being made?

The note is out of sync with functionality in BambooHR, which has a Job Title Specialty (Multi-Select) field:

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
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  • 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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