[llvm] workflows: Add a new job for packaging release sources (PR #91834)

[Tom Stellard via llvm-commits]

tstellar wrote:

> Hey @tstellar, awesome job working at this, it looks great!
> 
> If you allow me to drop a small nit pick, I'd suggest that you install the python dependencies for you build using the ["secure Install"](https://pip.pypa.io/en/stable/topics/secure-installs/) features -- That'd be a very similar change to what I did on #75859 . Of course that's not necessary, but would add an extra security layer to your release =)

I've created a new PR for this here: #92305 92305

https://github.com/llvm/llvm-project/pull/91834