Custom role UI enhancements

What does this MR do and why?

Some UI enhancements for displaying custom roles in group/project member pages:

Changes to the access level dropdown when inviting or editing members:

1. remove custom role aggregation by base access level and aggregate them together under Custom roles
2. increase the font weight of custom role names
3. add the role description for custom roles if there is one, limited to 2 lines

Before	After

Changes to the 'Max role' column in the members table:

1. when not editable, turn role name badges into plain text
2. add a tooltip with the role description to the role name when it is custom and not editable
3. remove custom ability badges for each of the enabled abilities when a custom role is assigned
4. add a Custom role badge when a custom role is assigned

Before	After

Issue: #437593 (closed)

How to set up and validate locally

1. Simulate SaaS
2. Create a namespace and apply the Ultimate license to the namespace
3. Visit http://localhost:3000/groups/#{group_name}/-/settings/roles_and_permissions and create a custom role with a long description
4. Visit http://localhost:3000/groups/#{group_name}/-/group_members and click Invite members