Monitoring service api (#2251)

## Issue Addressed

N/A

## Proposed Changes

Adds a client side api for collecting system and process metrics and pushing it to a monitoring service.

validator_client/src/config.rs

@@ -43,6 +43,8 @@ pub struct Config {
     pub http_api: http_api::Config,
     /// Configuration for the HTTP REST API.
     pub http_metrics: http_metrics::Config,
+    /// Configuration for sending metrics to a remote explorer endpoint.
+    pub monitoring_api: Option<monitoring_api::Config>,
 }
 
 impl Default for Config {
@@ -70,6 +72,7 @@ impl Default for Config {
             graffiti_file: None,
             http_api: <_>::default(),
             http_metrics: <_>::default(),
+            monitoring_api: None,
         }
     }
 }
@@ -233,6 +236,16 @@ impl Config {
 
             config.http_metrics.allow_origin = Some(allow_origin.to_string());
         }
+        /*
+         * Explorer metrics
+         */
+        if let Some(monitoring_endpoint) = cli_args.value_of("monitoring-endpoint") {
+            config.monitoring_api = Some(monitoring_api::Config {
+                db_path: None,
+                freezer_db_path: None,
+                monitoring_endpoint: monitoring_endpoint.to_string(),
+            });
+        }
 
         Ok(config)
     }