Create a deploy action

[pbarbarant]

Updates various gh actions and implements automatic deployment of the docs on a gh-pages branch.

[bthirion]

DO we need to merge in order to see if it works ?
@emdupre any comment ?

[pbarbarant]

DO we need to merge in order to see if it works ? @emdupre any comment ?

Yes in order to see the website, however we can check beforehand that the action completed successfully.

[emdupre]

Why this change ?

[pbarbarant]

I think it's better to be explicit about the format as sphinx can compile to various forms + it's consistent with other repos in Parietal-INRIA / mind-inria.

[pbarbarant]

Refactored the doc-build.yml with @emdupre to simplify the overall workflow. The website is now deployed from the gh-pages branch and will be automatically updated with every merge/push to the mainbranch.
BTW artifacts are also kept.

[emdupre]

Thanks, @pbarbarant ! When checks are green I'm good to merge 🚀

I already set up the redirect from https://parietal-inria.github.io/fmralign-docs and archived that repo, so I think this should be the end of our deployment issues ! 🎉

[bthirion]

Looks mostly good. Need to wait for CI to complete.

[pbarbarant]

Closes #91

[emdupre]

This is now the same error we saw before merging in 7dbab07 , so I think it's ready to go and I'm happy to see this in !

[pbarbarant]

Okay I'm merging it!