Rename and repurpose the "builder" repo

[andrew-sayers]

This repository is currently just for the container that builds the other repo's, but #1 would also make it a place for maintenance documentation. That seems like a mess, so I'd like to:

• rename this project to internal-tools
• move most of the existing files into a /builder subdirectory
• create a new dev-environment image that provides a one-click way to create a development environment
• put documentation in the sleepdiary.github.io repo, I guess in a directory called /docs/project-maintenance

@quinn-dev - the above would suggest your documentation will go in sleepdiary.github.io/docs, which would mean the discussion about the landing page will become a discussion about whether to point GitHub Pages to / or /docs in that repo. Let me know your thoughts, or I'll start pushing changes in a few days when I've got something to push.

[andrew-sayers]

I've now completed this repository's part of this issue, but will have to do the rest in the morning. The automated tests for any PRs that come in before then will probably fail, but that should sort itself out when I finish the job.

I'm closing this issue because everything left to discuss is better handled elsewhere. I'll write all that up once everything's working again.