Split invite groups into own modal

What does this MR do and why?

• separates invite members modal into invite groups and invite members.
  • see reasoning described in https://gitlab.com/gitlab-org/gitlab/-/issues/350800

Screenshots or screen recordings

no change

How to set up and validate locally

1. Enable the invite modal

   Feature.enable(:invite_members_group_modal)

2. Visit any group or project member pages such as http://127.0.0.1:3000/groups/flightjs/-/group_members
3. Click the Invite members button and invite.
4. Click the Invite a group button and invite.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #350800