API for LightClientBootstrap, LightClientFinalityUpdate, LightClientOptimisticUpdate and light client events (#3954)

* rebase and add comment

* conditional test

* test

* optimistic chould be working now

* finality should be working now

* try again

* try again

* clippy fix

* add lc bootstrap beacon api

* add lc optimistic/finality update to events

* fmt

* That error isn't occuring on my computer but I think this should fix it

* Add missing test file

* Update light client types to comply with Altair light client spec.

* Fix test compilation

* Support deserializing light client structures for the Bellatrix fork

* Move `get_light_client_bootstrap` logic to `BeaconChain`. `LightClientBootstrap` API to return `ForkVersionedResponse`.

* Misc fixes.
- log cleanup
- move http_api config mutation to `config::get_config` for consistency
- fix light client API responses

* Add light client bootstrap API test and fix existing ones.

* Fix test for `light-client-server` http api config.

* Appease clippy

* Efficiency improvement when retrieving beacon state.

---------

Co-authored-by: Jimmy Chen <jchen.tc@gmail.com>

common/eth2/src/lib.rs

@@ -667,6 +667,59 @@ impl BeaconNodeHttpClient {
         self.get_opt(path).await
     }
 
+    /// `GET beacon/light_client/bootstrap`
+    ///
+    /// Returns `Ok(None)` on a 404 error.
+    pub async fn get_light_client_bootstrap<E: EthSpec>(
+        &self,
+        block_root: Hash256,
+    ) -> Result<Option<ForkVersionedResponse<LightClientBootstrap<E>>>, Error> {
+        let mut path = self.eth_path(V1)?;
+
+        path.path_segments_mut()
+            .map_err(|()| Error::InvalidUrl(self.server.clone()))?
+            .push("beacon")
+            .push("light_client")
+            .push("bootstrap")
+            .push(&format!("{:?}", block_root));
+
+        self.get_opt(path).await
+    }
+
+    /// `GET beacon/light_client/optimistic_update`
+    ///
+    /// Returns `Ok(None)` on a 404 error.
+    pub async fn get_beacon_light_client_optimistic_update<E: EthSpec>(
+        &self,
+    ) -> Result<Option<ForkVersionedResponse<LightClientOptimisticUpdate<E>>>, Error> {
+        let mut path = self.eth_path(V1)?;
+
+        path.path_segments_mut()
+            .map_err(|()| Error::InvalidUrl(self.server.clone()))?
+            .push("beacon")
+            .push("light_client")
+            .push("optimistic_update");
+
+        self.get_opt(path).await
+    }
+
+    /// `GET beacon/light_client/finality_update`
+    ///
+    /// Returns `Ok(None)` on a 404 error.
+    pub async fn get_beacon_light_client_finality_update<E: EthSpec>(
+        &self,
+    ) -> Result<Option<ForkVersionedResponse<LightClientFinalityUpdate<E>>>, Error> {
+        let mut path = self.eth_path(V1)?;
+
+        path.path_segments_mut()
+            .map_err(|()| Error::InvalidUrl(self.server.clone()))?
+            .push("beacon")
+            .push("light_client")
+            .push("finality_update");
+
+        self.get_opt(path).await
+    }
+
     /// `GET beacon/headers?slot,parent_root`
     ///
     /// Returns `Ok(None)` on a 404 error.