Automatic merge from submit-queue (batch tested with PRs 39152, 39142, 39055)
Add test for json tags on internal and external types
Follow up from https://github.com/kubernetes/kubernetes/pull/38406
- adds static analysis tests preventing internal types from adding new json or protobuf tags
- adds static analysis tests requiring json tags on external types (and enforcing lower-case first letter)
- fixes issues found by the tests
59bd66ce3e