Optional include files

[Marko Kaznovac]

What is the problem you're trying to solve
I'd like to have optional include files to enable optional services override (e.g. developer specific configuration that should not be committed)

Describe the solution you'd like

include:
  - ../commons/compose.yaml
  - path: ../commons/compose-long.yaml
    project_directory: ..
    env_file: ../another/.env
  - ../another_domain/compose.yaml
  - path: ./docker-compose.local.yaml
    required: false # <-- propose to implement this --

services:
  webapp:
    # ...

Additional context
Similar solution to #240

But I'm not for the short optional syntax - as it hinders readability

[Guillaume Lours]

@kaznovac, what do you think of adding this specific include to an override file directly?