[lib] introduce community reducer

Summary:
This diff introduces the barebones community reducer and all the necessary logic to get it integrated into our codebase. Subsequent diffs will handle extending the community reducer to handle other cases we need to cover in our business logic

Linear task: https://linear.app/comm/issue/ENG-6159/introduce-community-reducer and https://linear.app/comm/issue/ENG-6535/start-processing-community-store-ops-on-sqllite

Depends on D11165

Test Plan:
Ran the following code + confirmed that a community was being added from this dispatched action

const dispatch = useDispatch();

const fakeCommunityID = '256|84261';

const onPressAddCommunity = React.useCallback(() => {
  const communityInfo: CommunityInfo = {
    enabledApps: {
      calendar: true,
      wiki: false,
      tasks: true,
      files: true,
    },
  };

  dispatch({
    type: addCommunityActionType,
    payload: {
      id: fakeCommunityID,
      newCommunityInfo: communityInfo,
    },
  });
}, [dispatch]);

Reviewers: atul, inka, kamil, tomek

Reviewed By: atul, kamil, tomek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11166