Update /rewards endpoints to match spec (#8967)

I believe one of our rewards endpoints is slightly out of spec. We do not return the `finalized` status for `post_beacon_rewards_attestations`.
Additionally, the `eth2` client doesn't expect the correct wrapper types for some other endpoints.


  - Update `post_beacon_rewards_attestations` server implementation to match spec.
- Update all three client functions in `eth2` to the correct wrapper type.
- Add missing tests for `http_api` to detect any regressions.


Co-Authored-By: Mac L <mjladson@pm.me>

beacon_node/http_api/src/lib.rs

@@ -1801,8 +1801,16 @@ pub fn serve<T: BeaconChainTypes>(
                     let execution_optimistic =
                         chain.is_optimistic_or_invalid_head().unwrap_or_default();
 
-                    Ok(api_types::GenericResponse::from(attestation_rewards))
-                        .map(|resp| resp.add_execution_optimistic(execution_optimistic))
+                    let finalized = epoch + 2
+                        <= chain
+                            .canonical_head
+                            .cached_head()
+                            .finalized_checkpoint()
+                            .epoch;
+
+                    Ok(api_types::GenericResponse::from(attestation_rewards)).map(|resp| {
+                        resp.add_execution_optimistic_finalized(execution_optimistic, finalized)
+                    })
                 })
             },
         );