Basic infrastructure: Add Dockerfile and basic testing for this repository

[cansavvy]

Description

I'm adding some initial github actions that will test and render things for us automatically as we work on this R package.

These are github actions I have used elsewhere but am adapting for here.

• docker-build.yml - this github action will manage our docker image for us
• pkgdown.yaml - This is a standard github action that will render our documentation for us
• style-code.yml this will re-run our test vignette whenever a pull request is opened to make sure the code we've written works on real data. It will also style our code
• R-CMD-check.yaml - this is a boilerplate gha that runs cheks to make sure the R package aspects of this code are up to code
• render-vignette.yml - this will re-render our vignette upon any changes to the main code base.

[cansavvy]

@howardbaek Most of the files here are pretty boilerplate, tried and true files we've used elsewhere. So while I don't need you to review this with a fine toothed comb, I do think you should review it to:

1. Get an understanding of the infrastructure here
2. See if there's any gaps in the file infrastructure I set up here.
3. Let me know anything I've done that doesn't make sense.

Note that there will likely be more than one function in each file in the R folder, I just put placeholders for now.