Added @matt-oakes as CODEOWNER of the ESLint package (facebook#27689)

Summary:
Adding myself as a code owner for the files in the ESLint package so I get email alerts for all PRs which alter the package.

This is needed because I need to manually publish updates to the package when pull requests are merged in. They are not handled by the standard React Native release cycle.

Related discussion: facebook#27085 (comment)

## Changelog

[Internal] [Added] - Added mat-oakes as a CODEOWNER for the ESLint package
Pull Request resolved: facebook#27689

Test Plan: N/A

Differential Revision: D19294768

Pulled By: cpojer

fbshipit-source-id: 3e3833261fc0b3c107b52b0e8232bd942a2ecaf4

.github/CODEOWNERS

@@ -35,3 +35,6 @@ Libraries/Text/* @shergin
 
 # These should not be modified through a GitHub PR
 LICENSE* @hramos @cpojer @yungsters
+
+# The eslint-config-react-native-community package requires manual publishing after merging
+/packages/eslint-config-react-native-community/* @matt-oakes