message: [gk] add code freeze gate keepers
  Closes:
diff: # Substribe to CI changes
  -/.circleci/ @libra/libra-oss-admin-team
  -/.github/ @libra/libra-oss-admin-team
  +# /.circleci/ @libra/libra-oss-admin-team
  +# /.github/ @libra/libra-oss-admin-team
  +
  # Subscribe to crypto crate changing PRs
  -/crypto @kchalkias @huitseeker @valerini
  +# /crypto @kchalkias @huitseeker @valerini
  +
  # Subscribe to potential JSON API changing PRs
  -/json-rpc/json-rpc-spec.md @thefallentree @xli
  -/json-rpc/types/ @thefallentree @xli
  -/json-rpc/src/methods.rs @thefallentree @xli
  -/client/ @thefallentree @xli
  +# /json-rpc/json-rpc-spec.md @thefallentree @xli
  +# /json-rpc/types/ @thefallentree @xli
  +# /json-rpc/src/methods.rs @thefallentree @xli
  +# /client/ @thefallentree @xli
  +
  # Subscribe to LCS format changes
  -/testsuite/generate-format/tests/staged/libra.yaml @thefallentree @matbd @xli
  +# /testsuite/generate-format/tests/staged/libra.yaml @thefallentree @matbd @xli
  +
  +# Code freeze
  +* @libra/release-gatekeepers
  