feat: allow theme file to be configurable

[mdonnalley]

Allow the location of the theme.json to be configured by the root CLI's package.json. This allows CLIs to ship a theme to their users

"files": ["theme.json"],
"oclif": {
  "theme": "./theme.json"
}

If users have their own theme at ~/.confg/<CLI>/theme.json then it will be merged in with the default theme, with the user theme taking precedence.

@W-14527856@

[mdonnalley]

@AllanOricil Thought you might be interested in this. We're finally getting to incorporating themes into sf. The plan is to have CLIs configure a default theme that ships with the CLI that users can override - either partially or entirely.

[AllanOricil]

It is time for the RGB version running at 60fps!