Calculate metapackage minimum version from sub-packages

In address #755, we went with the straightforward minimal bump #756 just to keep the ball rolling.

I'm repeating my comment on that PR here as a future potential enhancement:

I think, long term, we would benefit from calculating the min and max versions from the dependent packages...

Specifically, the minimum version is probably higher than 3.6, as, for example https://github.com/jupyter/notebook/blob/main/pyproject.toml is either 3.8 or higher (going by python-requires), or 3.9 or higher (going by Trove classifiers).