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>

beacon_node/src/config.rs

@@ -151,6 +151,9 @@ pub fn get_config<E: EthSpec>(
 
         client_config.http_api.duplicate_block_status_code =
             parse_required(cli_args, "http-duplicate-block-status")?;
+
+        client_config.http_api.enable_light_client_server =
+            cli_args.is_present("light-client-server");
     }
 
     if let Some(cache_size) = clap_utils::parse_optional(cli_args, "shuffling-cache-size")? {