Display SCIM identities in the identity table

What does this MR do and why?

For EE admins, SCIM identities are now shown under Admin > Overview > Users > USER > identity tab

Related to #294608 (closed)

Screenshots or screen recordings

How to set up and validate locally

Create SCIM identities using the bin/rails console:

group = Group.find_by_full_path('flightjs')
user = User.find_by_username('foo')
identity = ScimIdentity.create(group: group, user: user, active: true, extern_uid: user.username)

Go to the https://gdk.test:3443/admin/users/[foo]/identities

MR acceptance checklist

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