Add track-protocluster link (#108)

### Briefly, what does this PR introduce?

This PR introduces the `edm4eic::TrackProtoClusterLink`, a parallel to
the existing `edm4eic::TrackClusterMatch`. This functionality was
identified as missing during discussion of
[EICrecon#1669](eic/EICrecon#1699): in order to
ensure that merged/split clusters are reconstructed consistently with
other clusters it's preferable for the `TrackClusterMergeSplitter` to
output `edm4eic::ProtoCluster`s, but the connections between the
merged/split protoclusters and their antecedent tracks will need to be
propagated to downstream particle flow algorithms. This new type will
facilitate this.

### What kind of change does this PR introduce?
- [ ] Bug fix (issue #__)
- [X] New feature (issue #107 )
- [ ] Documentation update
- [ ] Other: __

### Please check if this PR fulfills the following:
- [ ] Tests for the changes have been added
- [ ] Documentation has been added / updated
- [X] Changes have been communicated to collaborators

### Does this PR introduce breaking changes? What changes might users
need to make to their code?

No.

### Does this PR change default behavior?

No.

---------

Co-authored-by: Dmitry Kalinkin <[email protected]>

Author: ruse-traveler

CMakeLists.txt

@@ -7,7 +7,7 @@ project(EDM4EIC
   LANGUAGES CXX)
 
 SET( ${PROJECT_NAME}_VERSION_MAJOR 8 )
-SET( ${PROJECT_NAME}_VERSION_MINOR 1 )
+SET( ${PROJECT_NAME}_VERSION_MINOR 2 )
 SET( ${PROJECT_NAME}_VERSION_PATCH 0 )
 SET( ${PROJECT_NAME}_VERSION  "${${PROJECT_NAME}_VERSION_MAJOR}.${${PROJECT_NAME}_VERSION_MINOR}.${${PROJECT_NAME}_VERSION_PATCH}" )
 

edm4eic.yaml

@@ -9,7 +9,7 @@
 ## If there are schema version changes that can be evolved, see the podio documentation
 ## for an example: https://github.com/AIDASoft/podio/tree/master/tests/schema_evolution
 ##
-schema_version: 801
+schema_version: 820
 
 options :
   # should getters / setters be prefixed with get / set?
@@ -600,3 +600,10 @@ datatypes:
     OneToOneRelations:
       - edm4eic::Cluster  cluster           // reference to the cluster
       - edm4eic::Track track                // reference to the track
+
+links:
+  edm4eic::TrackProtoClusterLink:
+    Description: "Link between a ProtoCluster and a Track"
+    Author: "D. Anderson, D. Kalinkin"
+    From: edm4eic::Track
+    To: edm4eic::ProtoCluster