[web] introduce community creation button for navigation sidebar

Summary:
This diff introduces the community creation button that will be rendered in the navigation sidebar footer

linear task: https://linear.app/comm/issue/ENG-5930/community-sidebar

Depends on D10362

Test Plan:
Please see the demo video below:

Reviewers: atul, rohan, kamil

Reviewed By: rohan

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10363