Upgrade discovery and restructure task execution (#1693)

* Initial rebase

* Remove old code

* Correct release tests

* Rebase commit

* Remove eth2-testnet dep on eth2libp2p

* Remove crates lost in rebase

* Remove unused dep

common/task_executor/src/metrics.rs

@@ -0,0 +1,21 @@
+/// Handles async task metrics
+use lazy_static::lazy_static;
+pub use lighthouse_metrics::*;
+
+lazy_static! {
+    pub static ref ASYNC_TASKS_COUNT: Result<IntGaugeVec> = try_create_int_gauge_vec(
+        "async_tasks_count",
+        "Total number of async tasks spawned using spawn",
+        &["async_task_count"]
+    );
+    pub static ref BLOCKING_TASKS_COUNT: Result<IntGaugeVec> = try_create_int_gauge_vec(
+        "blocking_tasks_count",
+        "Total number of async tasks spawned using spawn_blocking",
+        &["blocking_task_count"]
+    );
+    pub static ref BLOCKING_TASKS_HISTOGRAM: Result<HistogramVec> = try_create_histogram_vec(
+        "blocking_tasks_histogram",
+        "Time taken by blocking tasks",
+        &["blocking_task_hist"]
+    );
+}