Rename random to prev_randao (#3040)

## Issue Addressed

As discussed on last-night's consensus call, the testnets next week will target the [Kiln Spec v2](https://hackmd.io/@n0ble/kiln-spec).

Presently, we support Kiln V1. V2 is backwards compatible, except for renaming `random` to `prev_randao` in:

- https://github.com/ethereum/execution-apis/pull/180
- https://github.com/ethereum/consensus-specs/pull/2835

With this PR we'll no longer be compatible with the existing Kintsugi and Kiln testnets, however we'll be ready for the testnets next week. I raised this breaking change in the call last night, we are all keen to move forward and break things.

We now target the [`merge-kiln-v2`](https://github.com/MariusVanDerWijden/go-ethereum/tree/merge-kiln-v2) branch for interop with Geth. This required adding the `--http.aauthport` to the tester to avoid a port conflict at startup.

### Changes to exec integration tests

There's some change in the `merge-kiln-v2` version of Geth that means it can't compile on a vanilla Github runner. Bumping the `go` version on the runner solved this issue.

Whilst addressing this, I refactored the `testing/execution_integration` crate to be a *binary* rather than a *library* with tests. This means that we don't need to run the `build.rs` and build Geth whenever someone runs `make lint` or `make test-release`. This is nice for everyday users, but it's also nice for CI so that we can have a specific runner for these tests and we don't need to ensure *all* runners support everything required to build all execution clients.

## More Info

- [x] ~~EF tests are failing since the rename has broken some tests that reference the old field name. I have been told there will be new tests released in the coming days (25/02/22 or 26/02/22).~~

beacon_node/execution_layer/src/engine_api/json_structures.rs

@@ -64,7 +64,7 @@ pub struct JsonExecutionPayloadV1<T: EthSpec> {
     pub receipts_root: Hash256,
     #[serde(with = "serde_logs_bloom")]
     pub logs_bloom: FixedVector<u8, T::BytesPerLogsBloom>,
-    pub random: Hash256,
+    pub prev_randao: Hash256,
     #[serde(with = "eth2_serde_utils::u64_hex_be")]
     pub block_number: u64,
     #[serde(with = "eth2_serde_utils::u64_hex_be")]
@@ -91,7 +91,7 @@ impl<T: EthSpec> From<ExecutionPayload<T>> for JsonExecutionPayloadV1<T> {
             state_root,
             receipts_root,
             logs_bloom,
-            random,
+            prev_randao,
             block_number,
             gas_limit,
             gas_used,
@@ -108,7 +108,7 @@ impl<T: EthSpec> From<ExecutionPayload<T>> for JsonExecutionPayloadV1<T> {
             state_root,
             receipts_root,
             logs_bloom,
-            random,
+            prev_randao,
             block_number,
             gas_limit,
             gas_used,
@@ -130,7 +130,7 @@ impl<T: EthSpec> From<JsonExecutionPayloadV1<T>> for ExecutionPayload<T> {
             state_root,
             receipts_root,
             logs_bloom,
-            random,
+            prev_randao,
             block_number,
             gas_limit,
             gas_used,
@@ -147,7 +147,7 @@ impl<T: EthSpec> From<JsonExecutionPayloadV1<T>> for ExecutionPayload<T> {
             state_root,
             receipts_root,
             logs_bloom,
-            random,
+            prev_randao,
             block_number,
             gas_limit,
             gas_used,
@@ -165,7 +165,7 @@ impl<T: EthSpec> From<JsonExecutionPayloadV1<T>> for ExecutionPayload<T> {
 pub struct JsonPayloadAttributesV1 {
     #[serde(with = "eth2_serde_utils::u64_hex_be")]
     pub timestamp: u64,
-    pub random: Hash256,
+    pub prev_randao: Hash256,
     pub suggested_fee_recipient: Address,
 }
 
@@ -174,13 +174,13 @@ impl From<PayloadAttributes> for JsonPayloadAttributesV1 {
         // Use this verbose deconstruction pattern to ensure no field is left unused.
         let PayloadAttributes {
             timestamp,
-            random,
+            prev_randao,
             suggested_fee_recipient,
         } = p;
 
         Self {
             timestamp,
-            random,
+            prev_randao,
             suggested_fee_recipient,
         }
     }
@@ -191,13 +191,13 @@ impl From<JsonPayloadAttributesV1> for PayloadAttributes {
         // Use this verbose deconstruction pattern to ensure no field is left unused.
         let JsonPayloadAttributesV1 {
             timestamp,
-            random,
+            prev_randao,
             suggested_fee_recipient,
         } = j;
 
         Self {
             timestamp,
-            random,
+            prev_randao,
             suggested_fee_recipient,
         }
     }