Add group_scim_identity to the members API

What does this MR do and why?

Add group_scim_identity to the members API

Changelog: changed EE: true

References

• Extracted !193032 (merged)
• Expose SCIM identity in group-level UI (#354142 - closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create a top-level group
2. Set up group_saml
3. Associate SAML and SCIM identities to a user
   • Identity.new(user_id: user_id, provider: "group_saml", saml_provider_id: provider_id, extern_uid: "0x1234").save
   • GroupScimIdentity.new(group_id: group_id, user_id: user_id, active: true, extern_uid: "0x1234").save
4. Send a request to the Members API for the group

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