add preview mode for pull requests

[lucasraziel]

Added a PR Preview to CI using rossjrw/pr-preview-action@v1

closes #1491

[UlisesGascon]

Thanks for the proposal @lucasraziel!

I think we will need to have some capability of running previews from PRs generated in forks, but currently they are not supported:

This Action does not currently support deploying previews for PRs from forks.
See more details here

I don't have a lot of experience with Jekyll previews, but maybe something like gostatic can solve the preview problem: gostatic Jekyll GitHub Action. Since we will deploy the changes directly in a different environment (gostatic), what do you think about this approach?

I just found gostatic on a google search, so not sure if the new provider is the best option, but the free tier seems to cover out needs.

[lucasraziel]

I will check about It on next weekend and/or will look for other alternatives.

[jonchurch]

accepting this as it is would be destructive, so we cannot

our gh-pages branch is our main/production branch in this repo. this action commits to gh-pages to deploy previews under a preview dir namespace

the action does have the ability to commit the previews to a separate repo, which could work but is extra maintenance burden

[jonchurch]

Im planning to add netlify deploy previews since we can get those for free via their open source license. We can't leverage this repo's gh-pages for previews without committing to our production branch. This is going to have to be an integration, requiring admin perms, so I'll set it up.