Create out/soong/packaging directory and put a placeholder manifest

file in it.

This CL creates a manifest file under
out/soong/packaging/<suite>/<suite>.json

The content currently only contains the name of the test suite.
Further works will actually build the dependencies and generate
full manifest.

Change-Id: I0e69cd364e0a3a84159a5e4d2d21edd9fe2fdca1
Bug: 372945132