Support for flag --json to apollo service:list

[gtkatakura]

Sugestion

Would be awesome if we can pass a flag --json to apollo service:list to consume the output or have a programmatic version of apollo service:list to create nodejs scripts based on the output of this command.

Why

I want to create a variant schema based on another variant, to enable things like app reviews. The idea is to enable into PRs to publish an app review of a specific service and compose this service with the current staging schema.