Allow ava.config.json instead of package.json or CLI

[nowy]

Description

This is a feature request.

There are currently two ways of setting up ava config (prioritised):

1. CLI arguments
2. Package.json

Proposal: Add a third way, through ava.config.json

Advantages:

• Slimmer package.json file
• Easier to handle environment-specific config
• More flexibility on project configuration

Ie. This code in package.json, could be defined in ava.config.json

{
  "ava": {
  ...
  }
}

Also adding a flag to specify the config file (falling back to ava.config.json) if need be:

ava --config-file my.ava.config.json

Other technologies that handle this:

• TypeScript: https://www.typescriptlang.org/docs/handbook/tsconfig-json.html
• Webpack: https://webpack.js.org/configuration/configuration-types/

I would be willing to submit a PR if approved.
Thanks

[kevva]

This has been discussed in length in multiple issues already, e.g, #520.