CI: Support previews for multiple PRs

[Shaikh-Ubaid]

The current CI pushes the development deployment to https://github.com/lfortran/pull_request_preview and each push overrides the previous development deployment. This results in showing preview of only the lastest updated pull request at https://lfortran.github.io/pull_request_preview/.

We would like to see the preview for different pull requests simultaneously. This can be supported by having a unique folder for each pull request at https://github.com/lfortran/pull_request_preview/tree/gh-pages. The unique folder name could be taken from the pull request number. The preview for a pull request (for example) #1234 would then be available at https://lfortran.github.io/pull_request_preview/1234/.

Additionally, we would also like the unique folder to be deleted after a pull request is merged/closed (this can be supported over subsequent PRs).

[certik]

Yes, that would be nice.

Is the review served in the production site, or in a separate site? We should have it in a separate site, so that the production site is not re-deployed until merged into master. (Maybe it is already like that.)

[Shaikh-Ubaid]

Is the review served in the production site, or in a separate site? We should have it in a separate site, so that the production site is not re-deployed until merged into master. (Maybe it is already like that.)

Yes, the preview is served at https://lfortran.github.io/pull_request_preview/ which is different from the production site https://dev.lfortran.org/.

[certik]

Which github repository serves the production site and which repository serves the PR review?

[Shaikh-Ubaid]

Production Repository: https://github.com/lfortran/lcompilers_frontend (in branch gh-pages)
Production Url: https://dev.lfortran.org/

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Preview Repository: https://github.com/lfortran/pull_request_preview (in branch gh-pages)
Preview Url: https://lfortran.github.io/pull_request_preview/

[certik]

Ah, perfect, thank you. This is good. So all we need to do now is just serve it on different urls inside the https://github.com/lfortran/pull_request_preview which does not affect production in any way, so there is no problem.