hardhat-deploy-config: easier config (#3564)

Allow `paths` to be unset in the hardhat config.
The default path will be used if a top level `paths`
object is not included in the hardhat config.
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

.changeset/tender-items-sparkle.md

+---
+'@eth-optimism/hardhat-deploy-config': patch
+---
+
+Allow `paths` to be unset in hardhat config

packages/hardhat-deploy-config/src/plugin.ts

@@ -106,7 +106,7 @@ extendConfig(
   (config: HardhatConfig, userConfig: Readonly<HardhatUserConfig>) => {
     config.paths.deployConfig = normalizePath(
       config,
-      userConfig.paths.deployConfig,
+      userConfig.paths?.deployConfig,
       'deploy-config'
     )
   }