Add creation of TTL1 Containers to Overlay_tf.py

This merge request updates Overlay_tf.py to allow it to write out TTL1 Containers. This should mean that the output should in principle be the same as for OverlayPool_tf.py.
Added an ART test to confirm this. Once we are happy with how Overlay_tf.py is running we should adapt Reco_tf.py to use Overlay_tf.py rather than OverlayPool_tf.py.
Also fixed the Overlay_tf.py log output so that the event numbers and slots are displayed when running in AthenaMT mode.