Adding HGTD_Cluster and its TP converter
Splitting MR 42529 into parts. This one includes the addition of the HGTD_Cluster (that extends PrepRawData) and its TP converter.
Structures for the cluster collections and containers are also added, tests for TP converters run now. A simple structure for the converters has been chosen as discussed in the comments here and the the Upgrade SW meeting.
For reviewers (in case this is useful): As this MR contains several changes, I wanted to point out that the main focus here is the HGTD_PrepRawData/HGTD_Cluster class. This extends the tracking interface classes needed for reco in HGTD. The MR includes also the necessary "container" objects. The ClusterCollection contains all HGTD_Clusters on a given detector module, while the ClusterContainer contains all the collections in an event. The HGTD_EventTPCnv package contains the T/P converters for the HGTD_Cluster and its container. Tests are set up for both packages to test that things are working as expected.