[Stats] Metrics Export User Interface Part 1 (#9913)

* Metrics export port expose done.

* Support exposing metrics port + metrics agent service discovery through ray.nodes()

* Formatting.

* Added a doc.

* Linting.

* Change the location of metrics agent port.

* Addressed code review.

* Addressed code review.

python/ray/parameter.py

@@ -89,6 +89,8 @@ class RayParams:
         java_worker_options (list): The command options for Java worker.
         load_code_from_local: Whether load code from local file or from GCS.
         metrics_agent_port(int): The port to bind metrics agent.
+        metrics_export_port(int): The port at which metrics are exposed
+            through a Prometheus endpoint.
         _internal_config (str): JSON configuration for overriding
             RayConfig defaults. For testing purposes ONLY.
         lru_evict (bool): Enable LRU eviction if space is needed.
@@ -142,6 +144,7 @@ class RayParams:
                  _internal_config=None,
                  enable_object_reconstruction=False,
                  metrics_agent_port=None,
+                 metrics_export_port=None,
                  lru_evict=False):
         self.object_ref_seed = object_ref_seed
         self.redis_address = redis_address
@@ -181,6 +184,7 @@ class RayParams:
         self.java_worker_options = java_worker_options
         self.load_code_from_local = load_code_from_local
         self.metrics_agent_port = metrics_agent_port
+        self.metrics_export_port = metrics_export_port
         self.start_initial_python_workers_for_first_job = (
             start_initial_python_workers_for_first_job)
         self._internal_config = _internal_config