feat: add global configuration override file support

[tg90nor]

This allows specifying a configuration override file that will override chart and component defaults, but not environment overrides in the component.

My use case is I want to apply a global configuration to all components deployed to a particular environment, eg.:

ingressSuffix: 'staging.example.com'
environment:   'staging'

[royjs]

+1 for this. I have the exact same use case.

[zmalik]

Thanks @tg90nor LGTM