[native] [feature] [ENG-1016] add alert prompt to user, promote thread cant be undone

Summary:
add alert to let user know this action can't be undone

https://linear.app/comm/issue/ENG-1016/add-prompt-to-user-that-sidebar-promotion-cant-be-undone

Test Plan: go to promote thread, click cancel, click yes. Functionality should work as expected.

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

Reviewed By: palys-swm

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

Differential Revision: https://phabricator.ashoat.com/D3755