message: [docker] reduce docker size
  This commit uses one RUN cmd for operations that requires memory during build
  and operations that clear src and build dependencies to reduce the layers and
  docker image size.
diff: FROM ubuntu
  ENV DEBIAN_FRONTEND noninteractive
  +ENV PLATFORM ubuntu
  ENV RELEASE 1
  ENV NAT64 1
  ENV DNS64 1
  COPY . /app
  -
  WORKDIR /app
  -RUN apt-get update && apt-get install -y git lsb-core sudo
  +# Required during build or run
  +ENV OTBR_DOCKER_REQS sudo
  +
  +# Required during build, could be removed
  +ENV OTBR_DOCKER_DEPS git
  +
  +# Required and installed during build (script/bootstrap), could be removed
  +ENV OTBR_BUILD_DEPS \
  + apt-utils \
  + autoconf \
  + autoconf-archive \
  + automake \
  + build-essential \
  + ctags \
  + libtool \
  + wget
  +
  +# Required and installed during build (script/bootstrap) when RELEASE=1, could be removed
  +ENV OTBR_NORELEASE_DEPS \
  + cmake \
  + cpputest \
  + doxygen
  -RUN git reset --hard && git clean -xffd
  -RUN ./script/bootstrap && ./script/setup
  -RUN chmod 644 /etc/bind/named.conf.options
  -RUN mv ./script /tmp && mv ./etc /tmp
  -RUN find . -delete && rm -rf /usr/include
  -RUN mv /tmp/script . && mv /tmp/etc .
  -RUN apt-get autoremove -y -o APT::Autoremove::RecommendsImportant=0 -o APT::Autoremove::SuggestsImportant=0 && rm -rf /var/lib/apt/lists/*
  +RUN apt-get update \
  + && apt-get install -y $OTBR_DOCKER_REQS $OTBR_DOCKER_DEPS \
  + && git reset --hard && git clean -xffd \
  + && ./script/bootstrap \
  + && ./script/setup \
  + && chmod 644 /etc/bind/named.conf.options \
  + && mv ./script /tmp \
  + && mv ./etc /tmp \
  + && find . -delete \
  + && rm -rf /usr/include \
  + && mv /tmp/script . \
  + && mv /tmp/etc . \
  + && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false $OTBR_DOCKER_DEPS \
  + && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false $OTBR_BUILD_DEPS \
  + && ([ "${RELEASE}" = 1 ] || apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false "$OTBR_NORELEASE_DEPS";) \
  + && rm -rf /var/lib/apt/lists/*
  ENTRYPOINT ["/app/etc/docker/docker_entrypoint.sh"]
  