Add tracingstore route to export agglomerate graph as protobuf (#8872)

To be used by the python client, requested by @valentin-pinkau 

### URL of deployed dev instance (used for testing):
- https://agglomerategraphroute.webknossos.xyz

### Steps to test:
- Do some proofreading actions
- Request the new route, should return protobuf both for edited
agglomerates and non-edited agglomerates (should perform automatic
fallback lookup in the agglomerate file)

------
- [x] Added changelog entry (create a `$PR_NUMBER.md` file in
`unreleased_changes` or use `./tools/create-changelog-entry.py`)
- [x] Considered [common edge
cases](../blob/master/.github/common_edge_cases.md)

Author: fm3

unreleased_changes/8872.md

@@ -0,0 +1,2 @@
+### Added
+- Add tracingstore route to export agglomerate graph as protobuf, to be used by the python client.

webknossos-tracingstore/app/com/scalableminds/webknossos/tracingstore/controllers/EditableMappingController.scala

@@ -129,6 +129,26 @@ class EditableMappingController @Inject()(
       }
     }
 
+  def agglomerateGraph(tracingId: String, agglomerateId: Long, version: Option[Long]): Action[AnyContent] =
+    Action.async { implicit request =>
+      log() {
+        accessTokenService.validateAccessFromTokenContext(UserAccessRequest.readTracing(tracingId)) {
+          for {
+            annotationId <- remoteWebknossosClient.getAnnotationIdForTracing(tracingId)
+            tracing <- annotationService.findVolume(annotationId, tracingId, version)
+            _ <- editableMappingService.assertTracingHasEditableMapping(tracing)
+            remoteFallbackLayer <- volumeTracingService.remoteFallbackLayerForVolumeTracing(tracing, annotationId)
+            editableMappingInfo <- annotationService.findEditableMappingInfo(annotationId, tracingId)
+            agglomerateGraph <- editableMappingService.getAgglomerateGraphForIdWithFallback(editableMappingInfo,
+                                                                                            tracingId,
+                                                                                            tracing.version,
+                                                                                            agglomerateId,
+                                                                                            remoteFallbackLayer)
+          } yield Ok(agglomerateGraph.toByteArray).as(protobufMimeType)
+        }
+      }
+    }
+
   def agglomerateSkeleton(tracingId: String, agglomerateId: Long): Action[AnyContent] =
     Action.async { implicit request =>
       accessTokenService.validateAccessFromTokenContext(UserAccessRequest.readTracing(tracingId)) {

webknossos-tracingstore/conf/tracingstore.latest.routes

@@ -38,6 +38,7 @@ POST        /mapping/:tracingId/agglomeratesForSegments
 POST        /mapping/:tracingId/agglomerateGraphMinCut                              @com.scalableminds.webknossos.tracingstore.controllers.EditableMappingController.agglomerateGraphMinCut(tracingId: String)
 POST        /mapping/:tracingId/agglomerateGraphNeighbors                           @com.scalableminds.webknossos.tracingstore.controllers.EditableMappingController.agglomerateGraphNeighbors(tracingId: String)
 GET         /mapping/:tracingId/agglomerateSkeleton/:agglomerateId                  @com.scalableminds.webknossos.tracingstore.controllers.EditableMappingController.agglomerateSkeleton(tracingId: String, agglomerateId: Long)
+GET         /mapping/:tracingId/agglomerateGraph/:agglomerateId                     @com.scalableminds.webknossos.tracingstore.controllers.EditableMappingController.agglomerateGraph(tracingId: String, agglomerateId: Long, version: Option[Long])
 GET         /mapping/:tracingId/editedEdgesZip                                      @com.scalableminds.webknossos.tracingstore.controllers.EditableMappingController.editedEdgesZip(tracingId: String, version: Option[Long])
 
 # Zarr endpoints for volume annotations