Misc. dependency cleanup (#6810)

* remove ensure_dir_exists (2 deps saved)

* group UNHANDLED_ERRORs into a generic (2 deps saved)

* Introduce separate `health_metrics` crate

* separate health_metrics crate

* remove metrics from warp_utils

* move ProcessHealth::observe and SystemHealth::observe to health_metrics

* fix errors

* nitpick `Cargo.toml`s

---------

Co-authored-by: Daniel Knopik <daniel@dknopik.de>
# Conflicts:
#	Cargo.toml

common/monitoring_api/src/gather.rs

@@ -1,4 +1,5 @@
 use super::types::{BeaconProcessMetrics, ValidatorProcessMetrics};
+use health_metrics::observe::Observe;
 use metrics::{MetricFamily, MetricType};
 use serde_json::json;
 use std::collections::HashMap;

common/monitoring_api/src/lib.rs

@@ -4,6 +4,7 @@ use std::{path::PathBuf, time::Duration};
 
 use eth2::lighthouse::SystemHealth;
 use gather::{gather_beacon_metrics, gather_validator_metrics};
+use health_metrics::observe::Observe;
 use reqwest::{IntoUrl, Response};
 pub use reqwest::{StatusCode, Url};
 use sensitive_url::SensitiveUrl;