chore: add CODEOWNERS and repo config (#215)

.github/CODEOWNERS

@@ -0,0 +1,7 @@
+# Code owners file.
+# This file controls who is tagged for review for any given pull request.
+#
+# For syntax help see:
+# https://help.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners#codeowners-syntax
+
+*     @googleapis/gnostic

.github/sync-repo-settings.yaml

@@ -0,0 +1,17 @@
+rebaseMergeAllowed: true
+squashMergeAllowed: true
+mergeCommitAllowed: false
+branchProtectionRules:
+- pattern: master
+  isAdminEnforced: true
+  requiredStatusCheckContexts:
+    - 'continuous-integration/travis-ci'
+    - 'cla/google'
+  requiredApprovingReviewCount: 1
+  requiresCodeOwnerReviews: true
+  requiresStrictStatusChecks: true
+permissionRules:
+  - team: actools
+    permission: admin
+  - team: gnostic
+    permission: admin