Move validator http endpoints to a separate module (#8536)

Continuation of:
* #8529

Moving `/validator` endpoints out of `http_api` to a separation module. This should improve code maintainability, incremental compilation time and rust analyzer performance.

This is a tedious but straight forward change, so we're going with a pair & insta-merge approach to avoid painful & slow async review. @michaelsproul and I paired on the first commit - I believe we are almost done, will pair with @pawanjay176 tomorrow to wrap it up and merge tomorrow. (cc @macladson )


  


Co-Authored-By: Jimmy Chen <jchen.tc@gmail.com>

beacon_node/http_api/src/sync_committees.rs

@@ -1,6 +1,6 @@
 //! Handlers for sync committee endpoints.
 
-use crate::publish_pubsub_message;
+use crate::utils::publish_pubsub_message;
 use beacon_chain::sync_committee_verification::{
     Error as SyncVerificationError, VerifiedSyncCommitteeMessage,
 };