Create a "dev dependencies check" script for identifying what a contributor may need

[AetherUnbound]

Description

This came out of a discussion between maintainers about Sprints/Contributor Day events where new contributors could use some tooling to determine quickly what dependencies they'd need. This could be similar to calypso-doctor (although perhaps not as involved) in that it would check for various dependencies and fail for ones that are missing.

As just is an uncommon requirement for a project but happens to be necessary for everything we run on the command line, perhaps the tool could also auto-install just (by downloading a binary and putting it in the user's PATH) if requested.

This should probably be written in bash, or at least a language (like pure python) that doesn't require any dependencies in order to run on a POSIX machine.

The dependencies to check for (in my mind and from this doc) are:
0. git

1. just
2. docker
3. python (for pre-commit)
4. pnpm (for linting and the frontend)