feat: add CODEOWNERS (#472)

* add codeowners file

* docs: add ben to core-utils codeowners

.github/CODEOWNERS

+l2geth/                             @smartcontracts @tynes @karlfloersch
+ops/                                @tynes @karlfloersch
+packages/hardhat-ovm/               @smartcontracts
+packages/smock/                     @smartcontracts @maurelian
+packages/core-utils/                @smartcontracts @annieke @maurelian @ben-chain
+packages/core-utils/src/watcher.ts  @K-Ho
+packages/contracts/                 @smartcontracts @ben-chain @maurelian
+packages/message-relayer/           @K-Ho
+packages/batch-submitter/           @annieke @karlfloersch
+packages/data-transport-layer/      @annieke
+integration-tests/                  @tynes

CODEOWNERS.md

-packages/* @gakonst