Enable target specific filesystem view configuration

The cuttlestone target needs to have access to a subset of the
qcom-LA.UM.7.3-incoming projects. Due to a known build infrastructure
limitation we cannot include those projects multiple times.

Define a filesystem view that can be applied after the overlay.

Bug: 112560421
Test: `python development/keystone/overlay_test.py`
Test: `python development/keystone/container_test.py`
Test: `python development/keystone/container.py`
Change-Id: I6ae7fcd8bdb2fd835199967efc324d3a53b34eae