Deploy docs to GitHub Pages

[arnaucasau]

Summary

This PR changes the deploy-docs.yml workflow to deploy the documentation to GitHub Pages to migrate the project away from the qiskit.org domain.

More information about the change and a quick guide to set up GitHub pages can be found at: Qiskit/ecosystem#578

Reminder task for maintainers here to update the doc link in the About text for the repo on the main page once this change happens and the docs are re-deployed . This will need backporting to stable to have it apply to present docs version before it can be re-run.

• Update About text doc link

[woodsp-ibm]

FYI for CI failure see issue

• CI unit testing has failures under 3.12.1 #113

[ElePT]

Thanks Arnau for the PR, let's wait for testing-cabal/testtools#371 and see if the CI gets fixed once it's merged.

[woodsp-ibm]

Once this is done the first section in the README, about installation, will need its link updating.

[coveralls]

Pull Request Test Coverage Report for Build 7492816091

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 90.578%

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Totals
Change from base Build 7492731210:	0.0%
Covered Lines:	6470
Relevant Lines:	7143

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💛 - Coveralls

[woodsp-ibm]

@arnaucasau I have done a couple of workarounds to avoid the CI failures and as a result this can be moved forwards now. I think it's ready right.

Just as clarification, as I understand it, publishing is a 2 step process now, not just running this workflow. But now once its run the pages deployed to gh-pages need a second manual step to be published?

[arnaucasau]

Great, thank you @woodsp-ibm! Regarding your question, I guess when you say publish it, you mean to qiskit.org, but correct me if I'm wrong.

We only need the first of the two steps you mentioned. With this workflow, the docs will be deployed to GitHub Pages where the documentation will live, and once this change is done, I will set up the redirects from qiskit.org to the GitHub Pages link we have.

[woodsp-ibm]

@arnaucasau I was reading it was "deployed" to a gh-pages branch - maybe thats all that there is to it and its live from there and needs no extra step. Once its backported I'll run the workflow.

[arnaucasau]

Oh, I see what you meant now. Exactly, we only need to deploy to the gh-pages branch, and the publish step is done automatically by a workflow called pages-build-deployment. The only important thing is to set the branch correctly in the settings. Here you can find a short tutorial I wrote: Qiskit/ecosystem#578 (comment)

[woodsp-ibm]

@arnaucasau Ok, I ran the workflow, updated the Settings and the docs are now live https://qiskit-community.github.io/qiskit-algorithms/ I guess a redirect for former ecosystem url can be done now.