Implement ocaml wrapper around ReScript watch

[ghost]

We want commands to run before ReScript watch runs and after ReScript watch completes. The commands can use inotify wait to identify when to run, and can run ReScript build directly, instead of using ReScript watch. We might also want to control when next dev starts running.

#140 Generating pages will run after a ReScript build.

We will add a global.yaml data file and we want an ocaml process to convert this data into a globals ReScript module. This should occur before ReScript build runs.

This issue is related to #13.

This comment (#245 (comment)) may also be useful when thinking about the goals for this task.

[ghost]

In an ideal world, all the libraries we need would be available in ocaml, and the processing before ReScript build would produce ReScript modules with data and getStaticProps would consist of solely referencing the produced data. Ocaml would perform all the fetching and transforming, ReScript would only perform html rendering in react components.

[ghost]

Although this additional task does not need to be done at the same time, it would be nice to swap in https://github.com/hashicorp/next-remote-watch for next dev, as part of working on this issue.

[ghost]

I came up with a way to avoid #140. I don't think it's worth wrapping ReScript watch for the other noted feature (converting global data from yaml to ReScript constants). I am closing this for now.