Fixing headers.

...ib/security/credentials/composite/composite_credentials.h

src/core/lib/security/credentials/fake/fake_credentials.h

...y/credentials/google_default/google_default_credentials.h

src/core/lib/security/credentials/iam/iam_credentials.h

src/core/lib/security/credentials/jwt/jwt_credentials.h

...core/lib/security/credentials/oauth2/oauth2_credentials.h

...core/lib/security/credentials/plugin/plugin_credentials.h

src/core/lib/security/util/json_util.h

tools/dockerfile/grpc_clang_format/Dockerfile