Add flags for new home gardening mode

We're going to follow this new design for the home screen edit mode (home gardening): https://docs.google.com/presentation/d/1FOmmCdmGmSMR77_901IOMbvbPVxPmjaAdxZjy-D9tw0/edit#slide=id.g11f697f283a_0_0. This new design will be guarded by this flag.

Bug: 251259222
Test: manual
Change-Id: I36d0d1dddb463154140802b945dd092b072d6eaf