[feat][doc] PIP-264: Add OpenTelemetry messaging rate limit metrics r…

…eference (#943)

* [feat][doc] PIP-264: Add InflightReadsLimiter metrics

* [feat][doc] PIP-264: Add ServerCnxThrottleTracker metrics

docs/reference-metrics-opentelemetry.md

@@ -29,6 +29,17 @@ The number of connection create operations.
     * `success`
     * `failure`
 
+#### pulsar.broker.connection.rate_limit.count
+The number of times a connection has been rate limited.
+* Type: Counter
+* Unit: `{operation}`
+* Attributes:
+  * `pulsar.connection.rate_limit.operation.name` - The name of the rate limiting operation performed. Can be one of:
+    * `paused`
+    * `resumed`
+    * `throttled`
+    * `unthrottled`
+
 ### Topic Messaging metrics
 
 #### pulsar.broker.topic.subscription.count
@@ -669,6 +680,20 @@ The total number of mark delete operations for this ledger.
   * `pulsar.namespace` - The managed ledger namespace.
   * `pulsar.managed_ledger.name` - The name of the managed ledger.
 
+#### pulsar.broker.managed_ledger.inflight.read.limit
+Maximum number of bytes that can be retained by managed ledger data read from storage or cache.
+* Type: Counter
+* Unit: `By`
+
+#### pulsar.broker.managed_ledger.inflight.read.usage
+Estimated number of bytes retained by managed ledger data read from storage or cache.
+* Type: Counter
+* Unit: `By`
+* Attributes:
+  * `pulsar.managed_ledger.inflight.read.usage.state` - Indicates managed ledger memory limiter usage state. Can be one of:
+    * `used`
+    * `free`
+
 ### Schema Registry Metrics
 
 #### pulsar.broker.request.schema_registry.duration