[web] Show option to change role from the members modal

Summary:
As a first step in allowing admins to change member roles, the member panel option needed to be refactored to a more general approach to 'Change Role', as opposed to just toggling an admin status.

https://linear.app/comm/issue/ENG-4037/show-option-to-change-role-from-the-members-modal

Test Plan:
Confirm that the dropdown shows the updated icon and text

Reviewers: atul, ginsu

Reviewed By: atul

Subscribers: ted, ashoat, tomek

Differential Revision: https://phab.comm.dev/D8135