PLEASE NOTE THAT THIS DIFF AND SUBSEQUENT DIFFS IN THIS STACK WILL NOT BE LANDED UNTIL MORE OF THE REDESIGN IS READY SINCE THIS WILL CAUSE REGRESSIONS IN PROD

Now that useAddMembersListUserInfos has been introduced and returns all the necessary parts needed to use the checkbox add users list experience, we can now use the add users list instead of the old AddMembersListContent

Linear task: https://linear.app/comm/issue/ENG-5976/add-members-modal-experience

Depends on D10942

Please see the demo video below (please note there are some weird UI stuff that still needs to be polished up but a subsequent diff will fix that)