Support for more granular deployment options

[Chris Smith]

I have projects with multiple functions - some are running happily in production, but others are in development and just been put on staging. Is there a way to deploy specific functions to stage=prod? Its become cumbersome that we have to hold deployment of production-ready functions until everything's ready to go, or try to add disabling functionality to non-prudction-ready functions in case they're swept up in a deploy.

This could be done in the project settings.yml:

apps:
  - app1:
    stages:
      - qa
      - stg
      - prod
  - app2:
    stages:
      - qa
      - stg

[Madis Väin]

Multiregion deployments is also something that would be great to have.

A similar question here: #112