adds an adapted Containerfile from the product build

- all RPM builds happen in a multi-stage build
- this is just the first version of the Containerfile that I was able to get a passing build on, with `podman build -f Containerfile .`
- there are still several improvements to be implemented in the multi-stage build, to reduce some duplication. The previous build system didn't allow reusing previous build stages in subsequent ones (i.e. it didn't allow `FROM rpm-builder AS openresty`, etc.), so that still needs some clearing up.
- we should probably only keep one of `Containerfile` and `Dockerfile`. I just didn't overwrite the `Dockerfile` in one go to allow for a better chance of review.

Open issue: the jaegertracing-cpp-client RPM is currently commented out. That hadn't previously been ported to its own build stage and I don't know if it's worth doing that now. Hopefully, support for opentracing can be dropped in the next release (considering we now have support for opentelemetry).

Signed-off-by: Yorgos Saslis <[email protected]>