Add missing prometheus rules for persisted events (#8802)

The official dashboard uses data from these rules, but they were never added to the synapse-v2.rules. They are mentioned in this issue: https://github.com/matrix-org/synapse/issues/7917#issuecomment-661330409, but never got added to the rules.

Adding them results in all graphs in the "Event persist rate" section to function as intended.

Signed-off-by: Johanna Dorothea Reichmann <transcaffeine@finallycoffee.eu>

changelog.d/8802.doc

@@ -0,0 +1 @@
+Fix the "Event persist rate" section of the included grafana dashboard by adding missing prometheus rules.

contrib/prometheus/synapse-v2.rules

@@ -58,3 +58,21 @@ groups:
     labels:
       type: "PDU"
     expr: 'synapse_federation_transaction_queue_pending_pdus + 0'
+
+  - record: synapse_storage_events_persisted_by_source_type
+    expr: sum without(type, origin_type, origin_entity) (synapse_storage_events_persisted_events_sep{origin_type="remote"})
+    labels:
+      type: remote
+  - record: synapse_storage_events_persisted_by_source_type
+    expr: sum without(type, origin_type, origin_entity) (synapse_storage_events_persisted_events_sep{origin_entity="*client*",origin_type="local"})
+    labels:
+      type: local
+  - record: synapse_storage_events_persisted_by_source_type
+    expr: sum without(type, origin_type, origin_entity) (synapse_storage_events_persisted_events_sep{origin_entity!="*client*",origin_type="local"})
+    labels:
+      type: bridges
+  - record: synapse_storage_events_persisted_by_event_type
+    expr: sum without(origin_entity, origin_type) (synapse_storage_events_persisted_events_sep)
+  - record: synapse_storage_events_persisted_by_origin
+    expr: sum without(type) (synapse_storage_events_persisted_events_sep)
+