Create substitution for hyper links

[winksaville]

I'd like to be able to be able to make a substitution in an external hyperlink.
For example I'd like to be able to create a link to a specific version of a file:

So I would put the following in conf.py with the "normal" changes for sphinx-substitution-extensions:

rst_prolog = f".. |ver| replace:: {version}"

And then add the following to my .rst file:

Download the tarball_

.. _tarball: https://github.com/winksaville/py-taperable-helix/releases/v|ver|.tar.gz

And what I'd like is to see the "version" in the link:

Download the tarball_

.. _tarball guide: https://github.com/winksaville/py-taperable-helix/releases/v0.8.5.tar.gz