Standard gas limit api (#3450)

## Issue Addressed

Resolves https://github.com/sigp/lighthouse/issues/3403

## Proposed Changes

Implements https://ethereum.github.io/keymanager-APIs/#/Gas%20Limit

## Additional Info

N/A

Co-authored-by: realbigsean <sean@sigmaprime.io>

common/eth2/src/lighthouse_vc/http_client.rs

@@ -519,6 +519,18 @@ impl ValidatorClientHttpClient {
         Ok(url)
     }
 
+    fn make_gas_limit_url(&self, pubkey: &PublicKeyBytes) -> Result<Url, Error> {
+        let mut url = self.server.full.clone();
+        url.path_segments_mut()
+            .map_err(|()| Error::InvalidUrl(self.server.clone()))?
+            .push("eth")
+            .push("v1")
+            .push("validator")
+            .push(&pubkey.to_string())
+            .push("gas_limit");
+        Ok(url)
+    }
+
     /// `GET lighthouse/auth`
     pub async fn get_auth(&self) -> Result<AuthResponse, Error> {
         let mut url = self.server.full.clone();
@@ -598,11 +610,38 @@ impl ValidatorClientHttpClient {
         self.post_with_raw_response(url, req).await
     }
 
-    /// `POST /eth/v1/validator/{pubkey}/feerecipient`
+    /// `DELETE /eth/v1/validator/{pubkey}/feerecipient`
     pub async fn delete_fee_recipient(&self, pubkey: &PublicKeyBytes) -> Result<Response, Error> {
         let url = self.make_fee_recipient_url(pubkey)?;
         self.delete_with_raw_response(url, &()).await
     }
+
+    /// `GET /eth/v1/validator/{pubkey}/gas_limit`
+    pub async fn get_gas_limit(
+        &self,
+        pubkey: &PublicKeyBytes,
+    ) -> Result<GetGasLimitResponse, Error> {
+        let url = self.make_gas_limit_url(pubkey)?;
+        self.get(url)
+            .await
+            .map(|generic: GenericResponse<GetGasLimitResponse>| generic.data)
+    }
+
+    /// `POST /eth/v1/validator/{pubkey}/gas_limit`
+    pub async fn post_gas_limit(
+        &self,
+        pubkey: &PublicKeyBytes,
+        req: &UpdateGasLimitRequest,
+    ) -> Result<Response, Error> {
+        let url = self.make_gas_limit_url(pubkey)?;
+        self.post_with_raw_response(url, req).await
+    }
+
+    /// `DELETE /eth/v1/validator/{pubkey}/gas_limit`
+    pub async fn delete_gas_limit(&self, pubkey: &PublicKeyBytes) -> Result<Response, Error> {
+        let url = self.make_gas_limit_url(pubkey)?;
+        self.delete_with_raw_response(url, &()).await
+    }
 }
 
 /// Returns `Ok(response)` if the response is a `200 OK` response or a

common/eth2/src/lighthouse_vc/std_types.rs

@@ -10,6 +10,13 @@ pub struct GetFeeRecipientResponse {
     pub ethaddress: Address,
 }
 
+#[derive(Debug, Deserialize, Serialize, PartialEq)]
+pub struct GetGasLimitResponse {
+    pub pubkey: PublicKeyBytes,
+    #[serde(with = "eth2_serde_utils::quoted_u64")]
+    pub gas_limit: u64,
+}
+
 #[derive(Debug, Deserialize, Serialize, PartialEq)]
 pub struct AuthResponse {
     pub token_path: String,

common/eth2/src/lighthouse_vc/types.rs

@@ -138,3 +138,9 @@ pub struct Web3SignerValidatorRequest {
 pub struct UpdateFeeRecipientRequest {
     pub ethaddress: Address,
 }
+
+#[derive(Debug, Clone, PartialEq, Deserialize, Serialize)]
+pub struct UpdateGasLimitRequest {
+    #[serde(with = "eth2_serde_utils::quoted_u64")]
+    pub gas_limit: u64,
+}