Rationalize some ThreadPool Use in Snapshot Transport Actions (#54772) (#54782)

Removing a few spots where we clearly don't have to fork to the generic or management
pool since either we only interpret the current cluster state or fork-off directly to
some other pool in the transport action logic anyway.

server/src/main/java/org/elasticsearch/action/admin/cluster/repositories/get/TransportGetRepositoriesAction.java

@@ -60,7 +60,7 @@ public class TransportGetRepositoriesAction extends
 
     @Override
     protected String executor() {
-        return ThreadPool.Names.MANAGEMENT;
+        return ThreadPool.Names.SAME;
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/admin/cluster/repositories/verify/TransportVerifyRepositoryAction.java

@@ -56,7 +56,7 @@ public class TransportVerifyRepositoryAction extends
 
     @Override
     protected String executor() {
-        return ThreadPool.Names.MANAGEMENT;
+        return ThreadPool.Names.SAME;
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/create/TransportCreateSnapshotAction.java

@@ -52,9 +52,7 @@ public class TransportCreateSnapshotAction extends TransportMasterNodeAction<Cre
 
     @Override
     protected String executor() {
-        // Using the generic instead of the snapshot threadpool here as the snapshot threadpool might be blocked on long running tasks
+        return ThreadPool.Names.SAME;
-        // which would block the request from getting an error response because of the ongoing task
-        return ThreadPool.Names.GENERIC;
     }
 
     @Override