hardhat-node: add forking configuration

Adds forking config to the `ethereumoptimism/hardhat` docker image.
This can be configured with the following env vars:

- `FORK_URL` - http provider of the remote node to fetch data from
- `FORK_STARTING_BLOCK` - block to start forking from, if left
  undefined it will use the tip

Without `FORK_URL` set, it will not run in forking mode

Also adds the ability to configure the gas price with:

- `GAS_PRICE` - defaults to 0, which was the previous behavior

.changeset/rich-suits-drive.md

+---
+'@eth-optimism/hardhat-node': patch
+---
+
+Add fork mode config to ethereumoptimism/hardhat docker image

ops/docker-compose.yml

@@ -7,6 +7,8 @@ services:
     build:
       context: ./docker/hardhat
       dockerfile: Dockerfile
+    env_file:
+      -  ./envs/l1_chain.env
     ports:
         # expose the service to the host for integration testing
       - ${L1CHAIN_HTTP_PORT:-9545}:8545

ops/docker/hardhat/hardhat.config.js

-module.exports = {
+const isForkModeEnabled = !!process.env.FORK_URL
+const forkUrl = process.env.FORK_URL
+const forkStartingBlock = parseInt(process.env.FORK_STARTING_BLOCK) || undefined
+const gasPrice = parseInt(process.env.GAS_PRICE) || 0
+
+const config = {
   networks: {
     hardhat: {
-      gasPrice: 0,
+      gasPrice,
       initialBaseFeePerGas: 0
     },
   },
   analytics: { enabled: false },
 }
+
+if (isForkModeEnabled) {
+  console.log(`Running hardhat in a fork mode! URL: ${forkUrl}`)
+  if (forkStartingBlock) {
+    console.log(`Starting block: ${forkStartingBlock}`)
+  }
+  config.networks.hardhat.forking = {
+    url: forkUrl,
+    blockNumber: forkStartingBlock,
+  }
+} else {
+  console.log('Running with a fresh state...')
+}
+
+module.exports = config

ops/envs/l1_chain.env

+FORK_URL=
+FORK_STARTING_BLOCK=