[web] [feat] [ENG-991] add promote thread to menu dropdown

Summary:
add promote option to the dropdown menu, with API hook.

• The promote button shows in every dropdown. I need to add logic in another diff to only show it in sidebars that can be promoted.
• Loading state needs to be added in another diff too.

https://linear.app/comm/issue/ENG-991/promote-sidebar-to-subthread-on-web

Test Plan: click menu, it should show, doesn't do anything yet

Reviewers: atul, yayabosh, def-au1t, palys-swm

Reviewed By: def-au1t, palys-swm

Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3731