Enhanced shared configuration

[gitfool]

Is your feature request related to a problem? Please describe.

Following up from https://github.com/intuit/auto/issues/191, add support for something like preset hosting and local presets (for self-hosted ghes), which I use with renovate.

Describe the solution you'd like

I'd like to be able to share auto config by checking in a config per repo that simply points to this shared config (and allows extending it). For example, with renovate I can have the following config in a ghes repo, which causes renovate to load the config directly from ghes:

{
  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
  "extends": [
    "config:base",
    "local>owner/repo:renovate-default"
  ]
}

The config can also be customized further by adding repo specific sections.

Describe alternatives you've considered

• Copy the same config across all repos
  • Drifts from ideally shared config over time
• Download the config before running auto in a GitHub Action
  • Must be downloaded to repo root (runner working directory) and added to .gitignore; messy to customize

Additional context

[hipstersmoothie]

This is a pretty cool idea. I like that it enables shared config from non npm projects too!