added prdoc

Signed-off-by: Iulian Barbu <iulian.barbu@parity.io>

prdoc/pr_5572.prdoc

@@ -0,0 +1,16 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: added RPC metrics for the collator
+
+doc:
+  - audience: [ Node Dev, Node Operator ]
+    description: |
+      The metrics are names `cumulus_rpc_request_{method}` and can be scraped by prometheus agents from the relaychain minimal node's prometheus exporter. The metrics provide information about `count`, `sum` and `duration` in seconds (with exponential buckets with parameters as start = 0.001, factor = 4, count = 9).
+crates: 
+  - name: cumulus-relay-chain-rpc-interface
+    bump: minor
+  - name: cumulus-relay-chain-minimal-node
+    bump: minor
+  - name: cumulus-test-service
+    bump: patch