Index classify-patch task in the Taskcluster index by diff ID

Fixes #668

infra/taskcluster-hook-classify-patch.json

@@ -55,7 +55,9 @@
         "retries": 5,
         "routes": [
             "notify.email.release-mgmt-analysis@mozilla.com.on-failed",
-            "notify.irc-channel.#bugbug.on-failed"
+            "notify.irc-channel.#bugbug.on-failed",
+            "index.project.relman.bugbug.classify_patch.latest",
+            "index.project.relman.bugbug.classify_patch.diff.${payload['DIFF_ID']}"
         ],
         "schedulerId": "-",
         "scopes": [