/usr/share/vim/vimfiles/syntax/dockerfile.vim

syntax match dockerfileKeyword /\v^\s*(ONBUILD\s+)?(ADD|ARG|CMD|COPY|ENTRYPOINT|ENV|EXPOSE|FROM|HEALTHCHECK|LABEL|MAINTAINER|RUN|SHELL|STOPSIGNAL|USER|VOLUME|WORKDIR)\s/

syntax region shLine matchgroup=dockerfileKeyword start=/\v^\s*(RUN|CMD|ENTRYPOINT)\s/ end=/\v$/ contains=@SH

!!!
ARG
LABEL
ENV

COPY --chown=app ...