create TrackSeed structure to store the seed info (#69)

### Briefly, what does this PR introduce?
Create TrackSeed structure to store the seed info

### What kind of change does this PR introduce?
- [ ] Bug fix (issue #__)
- [x] New feature (issue #__)
- [ ] 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 breaking change. Corresponding EICrecon algorithms will be updated to
use the data structure. No impact until then.
### Does this PR change default behavior?
N/A

---------

Co-authored-by: Wouter Deconinck <[email protected]>

edm4eic.yaml

@@ -370,6 +370,15 @@ datatypes:
     OneToManyRelations:
       - edm4eic::TrackerHit hits            // Hits in this measurement (single or clustered)
 
+  edm4eic::TrackSeed:
+    Description: "Seed info from the realistic seed finder"
+    Author: "S. Li, B. Schmookler, J. Osborn"
+    Members:
+      - edm4hep::Vector3f         perigee   // Vector for the perigee (line surface)
+    OneToManyRelations:
+      - edm4eic::TrackerHit       hits      // Tracker hits triplet for seeding
+    OneToOneRelations:
+      - edm4eic::TrackParameters  params    // Initial track parameters
 
   edm4eic::Trajectory:
     Description: "Raw trajectory from the tracking algorithm. What is called hit here is 2d measurement indeed."
@@ -388,7 +397,9 @@ datatypes:
       - edm4eic::TrackParameters trackParameters            // Associated track parameters, if any
       - edm4eic::Measurement2D measurements_deprecated      // Measurements that were used for this track. Will move this to the edm4eic::Track
       - edm4eic::Measurement2D outliers_deprecated          // Measurements that were not used for this track. Will move this to the edm4eic::Track
-
+    OneToOneRelations:
+      - edm4eic::TrackSeed      seed      // Corresponding track seed
+
   edm4eic::TrackParameters:
     Description: "ACTS Bound Track parameters"
     Author: "W. Armstrong, S. Joosten, J. Osborn"