Simplify import process for Cloud -> Local data imports

Importing data from cloud environments into your local environment is a bit complex currently. We want to simplify this down to improve the user experience.

@joehoyle has existing work started at https://github.com/humanmade/altis-local-server/pull/345 but this was for Local Server rather than generically across our local environments.

As a developer, I want to import cloud exports with a single, simple command so that I don't need to read long documentation every time.

* [ ] Running a single command (with a parameter of an export file) imports the exported data
* [ ] Database is imported and automatically search-replace'd
* [ ] Uploads are imported (i.e. via `import-uploads` for Local Server)
* [ ] Command works across both Local Server and Local Chassis
* [ ] Command supports backups containing data-only, uploads-only, or both
* [ ] Command outputs useful help text if used without export file parameter
* [ ] Command outputs only machine-readable output when passing `--porcelain`