HltEventLoopMgr: Record ByteStreamMetadataContainer instead of ByteStreamMetadata

Adapt HltEventLoopMgr to recent changes in BS metadata done when moving from EventInfo to xAOD::EventInfo BS converter. Now BS metadata are recorded in a container rather than just an object directly.

Fixes these warnings:

InputMetaDataStore                      1   0   WARNING retrieve(const): No valid proxy for object ByteStreamMetadata  of type ByteStreamMetadataContainer(CLID 1076128893) 
EventInfoByteStreamAuxCnv               1   0   WARNING Unable to retrieve Input MetaData for ByteStream 

seen e.g. here: https://atlas-art-data.web.cern.ch/atlas-art-data/build-output/master/Athena/x86_64-slc6-gcc8-opt/2019-08-12T2131/TrigP1Test/test_trigP1_py_CalibPeb_build/Warnings.log

cc @tsulaia, @ssnyder, @akraszna, @fwinkl, @wiedenma