Add option to run specific commands depending on the operative system

[acostapazo]

First approach

Install

install:
  run_ubuntu:
    - sudo apt update
    - sudo apt install myprogram
  run_macos:
    - brew install myprogram
  run:
    - echo "Hello"

Steps

clean:
  run_ubuntu:
    - sudo apt update
    - sudo apt install myprogram
  run_macos:
    - brew install myprogram
  run:
    - echo "Hello"

We should implement it respecting the definition order of the runs.

[acostapazo]

I'd prefer the one proposed by @fgsalomon

install:
  run:
    ubuntu:
       - sudo apt update
       - sudo apt install myprogram
     macos:
       - brew install myprogram
     all:
      - echo "Hello"