[native] Display "Skip"/"Done" button to exit community creation flow

Summary:
We add a "Skip"/"Done" LinkButton to CommunityCreationMembers to exit the community creation flow once user is done (potentially) selecting users.

This diff handles the "Skip" case, where we just navigate back to ChatThreadListRouteName.

Next diff will handle the "Done" case where we have users we want to hit add_users endpoint with.

Diff after that will handle navigating to the thread corresponding to the newly created community.

Test Plan: Pressing "Skip"/"Done" exits flow as expected.

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8115