Add ONBUILD to ARGs to allow usage in child builds

[Archie-Elvie]

This will allow people to extend the current base image and use the same arguments.

For example., if I do the following:

FROM zephyrprojectrtos/ci:latest
RUN apt install -y clang-format-$LLVM_VERSION`

This does not work as the $LLVM_VERSION ARG is not passed to the child dockerfile. This can be implemented with the ONBUILD keyword.

Proposed change:

ONBUILD ARG ZSDK_VERSION=0.14.2
ONBUILD ARG DOXYGEN_VERSION=1.9.4
ONBUILD ARG CMAKE_VERSION=3.20.5
ONBUILD ARG RENODE_VERSION=1.13.0
ONBUILD ARG LLVM_VERSION=12
ONBUILD ARG BSIM_VERSION=v1.0.3
ONBUILD ARG WGET_ONBUILD ARGS="-q --show-progress --progress=bar:force:noscroll --no-check-certificate"