Builder Specs v0.2.0 (#3134)

## Issue Addressed

https://github.com/sigp/lighthouse/issues/3091

Extends https://github.com/sigp/lighthouse/pull/3062, adding pre-bellatrix block support on blinded endpoints and allowing the normal proposal flow (local payload construction) on blinded endpoints. This resulted in better fallback logic because the VC will not have to switch endpoints on failure in the BN <> Builder API, the BN can just fallback immediately and without repeating block processing that it shouldn't need to. We can also keep VC fallback from the VC<>BN API's blinded endpoint to full endpoint.

## Proposed Changes

- Pre-bellatrix blocks on blinded endpoints
- Add a new `PayloadCache` to the execution layer
- Better fallback-from-builder logic

## Todos

- [x] Remove VC transition logic
- [x] Add logic to only enable builder flow after Merge transition finalization
- [x] Tests
- [x] Fix metrics
- [x] Rustdocs


Co-authored-by: Mac L <mjladson@pm.me>
Co-authored-by: realbigsean <sean@sigmaprime.io>

validator_client/src/config.rs

@@ -52,7 +52,12 @@ pub struct Config {
     /// If true, enable functionality that monitors the network for attestations or proposals from
     /// any of the validators managed by this client before starting up.
     pub enable_doppelganger_protection: bool,
-    pub private_tx_proposals: bool,
+    /// Enable use of the blinded block endpoints during proposals.
+    pub builder_proposals: bool,
+    /// Overrides the timestamp field in builder api ValidatorRegistrationV1
+    pub builder_registration_timestamp_override: Option<u64>,
+    /// Fallback gas limit.
+    pub gas_limit: Option<u64>,
     /// A list of custom certificates that the validator client will additionally use when
     /// connecting to a beacon node over SSL/TLS.
     pub beacon_nodes_tls_certs: Option<Vec<PathBuf>>,
@@ -91,7 +96,9 @@ impl Default for Config {
             monitoring_api: None,
             enable_doppelganger_protection: false,
             beacon_nodes_tls_certs: None,
-            private_tx_proposals: false,
+            builder_proposals: false,
+            builder_registration_timestamp_override: None,
+            gas_limit: None,
             strict_fee_recipient: false,
         }
     }
@@ -300,8 +307,27 @@ impl Config {
             config.enable_doppelganger_protection = true;
         }
 
-        if cli_args.is_present("private-tx-proposals") {
-            config.private_tx_proposals = true;
+        if cli_args.is_present("builder-proposals") {
+            config.builder_proposals = true;
+        }
+
+        config.gas_limit = cli_args
+            .value_of("gas-limit")
+            .map(|gas_limit| {
+                gas_limit
+                    .parse::<u64>()
+                    .map_err(|_| "gas-limit is not a valid u64.")
+            })
+            .transpose()?;
+
+        if let Some(registration_timestamp_override) =
+            cli_args.value_of("builder-registration-timestamp-override")
+        {
+            config.builder_registration_timestamp_override = Some(
+                registration_timestamp_override
+                    .parse::<u64>()
+                    .map_err(|_| "builder-registration-timestamp-override is not a valid u64.")?,
+            );
         }
 
         if cli_args.is_present("strict-fee-recipient") {