Make clear that the config has changed since prometheus v2

This restores the config that is usable for prometheus pre v2.0.0
The new config only works for Prometheus v2+

contrib/prometheus/synapse-v2.rules

@@ -0,0 +1,60 @@
+groups:
+- name: synapse
+  rules:
+  - record: "synapse_federation_transaction_queue_pendingEdus:total"
+    expr: "sum(synapse_federation_transaction_queue_pendingEdus or absent(synapse_federation_transaction_queue_pendingEdus)*0)"
+  - record: "synapse_federation_transaction_queue_pendingPdus:total"
+    expr:   "sum(synapse_federation_transaction_queue_pendingPdus or absent(synapse_federation_transaction_queue_pendingPdus)*0)"
+  - record: 'synapse_http_server_requests:method'
+    labels:
+      servlet: ""
+    expr: "sum(synapse_http_server_requests) by (method)"
+  - record: 'synapse_http_server_requests:servlet'
+    labels:
+      method: ""
+    expr: 'sum(synapse_http_server_requests) by (servlet)'
+
+  - record: 'synapse_http_server_requests:total'
+    labels:
+      servlet: ""
+    expr: 'sum(synapse_http_server_requests:by_method) by (servlet)'
+
+  - record: 'synapse_cache:hit_ratio_5m'
+    expr: 'rate(synapse_util_caches_cache:hits[5m]) / rate(synapse_util_caches_cache:total[5m])'
+  - record: 'synapse_cache:hit_ratio_30s'
+    expr: 'rate(synapse_util_caches_cache:hits[30s]) / rate(synapse_util_caches_cache:total[30s])'
+
+  - record: 'synapse_federation_client_sent'
+    labels:
+      type: "EDU"
+    expr: 'synapse_federation_client_sent_edus + 0'
+  - record: 'synapse_federation_client_sent'
+    labels:
+      type: "PDU"
+    expr: 'synapse_federation_client_sent_pdu_destinations:count + 0'
+  - record: 'synapse_federation_client_sent'
+    labels:
+      type: "Query"
+    expr: 'sum(synapse_federation_client_sent_queries) by (job)'
+
+  - record: 'synapse_federation_server_received'
+    labels:
+      type: "EDU"
+    expr: 'synapse_federation_server_received_edus + 0'
+  - record: 'synapse_federation_server_received'
+    labels:
+      type: "PDU"
+    expr: 'synapse_federation_server_received_pdus + 0'
+  - record: 'synapse_federation_server_received'
+    labels:
+      type: "Query"
+    expr: 'sum(synapse_federation_server_received_queries) by (job)'
+
+  - record: 'synapse_federation_transaction_queue_pending'
+    labels:
+      type: "EDU"
+    expr: 'synapse_federation_transaction_queue_pending_edus + 0'
+  - record: 'synapse_federation_transaction_queue_pending'
+    labels:
+      type: "PDU"
+    expr: 'synapse_federation_transaction_queue_pending_pdus + 0'