feat: upgrade project/schema version to v8.7.0 (#153)

### Briefly, what does this PR introduce?
This PR upgrades the project and schema version to the next release.
(Note: branch renamed to avoid ref clash with future release tag name.)

Author: wdconinc

CMakeLists.txt

@@ -7,7 +7,7 @@ project(EDM4EIC
   LANGUAGES CXX)
 
 SET( ${PROJECT_NAME}_VERSION_MAJOR 8 )
-SET( ${PROJECT_NAME}_VERSION_MINOR 6 )
+SET( ${PROJECT_NAME}_VERSION_MINOR 7 )
 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: 860
+schema_version: 870
 
 options :
   # should getters / setters be prefixed with get / set?