fix: Set group name and number columns to handle Safari [DET-9948] [DET-9949]

[mapmeld]

Description

On Safari, the group admin page wasn't showing group names
We researched and found Safari/WebKit uses width: intrinsic instead of fit-content

After discussion on Slack about this ticket and #8309 , best option is 100% width

We also added parentheses around the number of groups or users

Test Plan

On /det/admin/user-management,

With EE backend, group name column appears on Safari without issues

Users and Groups tabs appear with a number in parentheses. (If groups is undefined, the Group parentheses and number do not appear)

Checklist

• Changes have been manually QA'd
• User-facing API changes need the "User-facing API Change" label.
• Release notes should be added as a separate file under docs/release-notes/.
  See Release Note for details.
• Licenses should be included for new code which was copied and/or modified from any external code.

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[mapmeld]

Updated test plan; thanks for the suggested change