Install podio edm

[DraTeots]

In order to inherit experiment EDM from Acts EDM one has to do something like this:

PODIO_GENERATE_DATAMODEL(myedm myedm .yaml headers sources
  UPSTREAM_EDM edm4hep:${ACTS_EDM_DATA_DIR}/edm.yaml
  IO_BACKEND_HANDLERS ${PODIO_IO_HANDLERS}
  OUTPUT_FOLDER ${CMAKE_CURRENT_BINARY_DIR}
  )

The problem is that edm.yaml is not being installed anywhere.

Providing something like ACTS_EDM_DATA_DIR or maybe directly ACTS_PODIO_EDM_YAML variable in cmake config would also simplify life and appreciated.