[web] Create a modal that allows admins to change a member's role (dropdown menu, actionable buttons)
Summary:
This is the second part of the modal creation, utilizing the earlier Dropdown component and creating the two 'back' and 'save' buttons. Functionality for these buttons will be added up the stack to
make this diff easier to review.
https://linear.app/comm/issue/ENG-4038/create-a-modal-that-allows-admins-to-change-a-members-role
Depends on D8137
Test Plan:
Please see a screenshot of what the complete modal looks like now
Reviewers: atul, ginsu
Reviewed By: atul
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D8138