[native] Introduce communityCreationButton to CommunityDrawerContent

Summary:
Add community creation button to community selection drawer.

Just layout/styling for now, functionality will be added in subsequent diff.

Test Plan:
Looks as expected (dark mode):

Looks as expected (light mode):

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: ted, tomek

Differential Revision: https://phab.comm.dev/D7924