Update links to documentations in the tutorials

[horizon-blue]

In this PR I replaced all occurrences of "probcomp.github.io/Gen/dev" with "www.gen.dev/docs/stable", which is essentially equivalent to the changes in probcomp/gen-quickstart#91

(it will be nice if we can automatically sync the changes from gen-quickstart to the gh-pages branch of this main repo in the future).

[ztangent]

Thank you!! I think we will also need to make the URL changes that were made in this PR to gen-quickstart, because the changes there never got synced to this branch.

Agreed that it'd be best to automatically sync the changes, but I'm not sure how to do that -- we'd somehow need to set up a Github Action that downloads the source code from gen-quickstart, compiles the Jupyter Notebooks into Markdown files, and then push to the gh-pages branch on this repository, which seems non trivial. I had been thinking that we could just do it manually this time around, but directly making these edits is also fine since it's a small change.

[horizon-blue]

Thanks for the quick review, @ztangent! Yeah, I agree that cross-repo syncing can be a bit tricky to handle.

Just to clarify, do you mean that there are additional changes that I should make in this PR (or to gen-quickstart in addition to what's been covered in probcomp/gen-quickstart#91)?

[ztangent]

Oops, I forgot to paste the link 🤦. I meant that there are URL changes made in this PR (probcomp/gen-quickstart#90) that we should also make in the Gen.jl repo.

[horizon-blue]

Gotcha! I just updated this PR to replace all "www.gen.dev/dev/" with "www.gen.dev/docs/dev/" as well :)

[ztangent]

Looks great to me!