docker/windows: create a rust image for gst-rs
Create an image on top of the existing windows image, where it has a version of gstreamer per-installed as well as a rust toolchain so it can be used for the gst-rs CI.
Based on the build image for the existing windows jobs, add an image with rust toolchain and a (stable) gstreamer install for the bindings to build against. See https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/merge_requests/701
docker/windows: build rust image in the ci This makes it a bit harder to build an image locally with the script, as now the rust image requires to pass it the base image tag as a --build-arg. This way though we don't need to duplicate and keep the string of the image in sync. Another thing is that now the docker windows image build is properly passing/replacing build args and we can build non-master versions of the image too.
docker/windows: build two version of the rust image Build 2 images with different rust toolchains so we can test both the latest release, as well as the minimum supported compiler version and catch regressions.