Payload envelope db operations (#8717)

Adds support for payload envelopes in the db. This is the minimum we'll need to store and fetch payloads.


  


Co-Authored-By: Eitan Seri- Levi <eserilev@gmail.com>

beacon_node/store/src/impls.rs

@@ -1 +1,2 @@
 pub mod execution_payload;
+mod signed_execution_payload_envelope;