exchangeCapabilities & Capella Readiness Logging (#3918)

* Undo Passing Spec to Engine API

* Utilize engine_exchangeCapabilities

* Add Logging to Indicate Capella Readiness

* Add exchangeCapabilities to mock_execution_layer

* Send Nested Array for engine_exchangeCapabilities

* Use Mutex Instead of RwLock for EngineCapabilities

* Improve Locking to Avoid Deadlock

* Prettier logic for get_engine_capabilities

* Improve Comments

* Update beacon_node/beacon_chain/src/capella_readiness.rs

Co-authored-by: Michael Sproul <micsproul@gmail.com>

* Update beacon_node/beacon_chain/src/capella_readiness.rs

Co-authored-by: Michael Sproul <micsproul@gmail.com>

* Update beacon_node/beacon_chain/src/capella_readiness.rs

Co-authored-by: Michael Sproul <micsproul@gmail.com>

* Update beacon_node/beacon_chain/src/capella_readiness.rs

Co-authored-by: Michael Sproul <micsproul@gmail.com>

* Update beacon_node/beacon_chain/src/capella_readiness.rs

Co-authored-by: Michael Sproul <micsproul@gmail.com>

* Update beacon_node/client/src/notifier.rs

Co-authored-by: Michael Sproul <micsproul@gmail.com>

* Update beacon_node/execution_layer/src/engine_api/http.rs

Co-authored-by: Michael Sproul <micsproul@gmail.com>

* Addressed Michael's Comments

---------

Co-authored-by: Michael Sproul <micsproul@gmail.com>

beacon_node/beacon_chain/src/test_utils.rs

@@ -375,7 +375,6 @@ where
             .collect::<Result<_, _>>()
             .unwrap();
 
-        let spec = MainnetEthSpec::default_spec();
         let config = execution_layer::Config {
             execution_endpoints: urls,
             secret_files: vec![],
@@ -386,7 +385,6 @@ where
             config,
             self.runtime.task_executor.clone(),
             self.log.clone(),
-            &spec,
         )
         .unwrap();