Add an option to disable output buffering

[jigarius]

Motivation

• Currently, Drall uses amphp/process libraries to execute commands in parallel.
• This means the output of every command is buffered and then displayed when the command finishes.
• In some scenarios, say, when running with only 1 worker, the user might be interested in seeing the command output in realtime instead.
  • This also helps in debugging Drall.
• Maybe we could use a parameter, say, --drall-no-buffer that would force Drall to throw all output to the console instead of collecting it in a variable.

Tasks

• Upgrade amphp/* libraries to 2.x.
  • The newer version seems easier to use and understand.
• Create option: --no-buffer, -B.

[jigarius]

Instead of duplicating the code execution logic, I was checking if this can be done through the Amphp libraries, however, I think it will take more time and research that I had initially thought. For now, I'll leave this open. Any ideas or help is welcome. I'd prefer to have the commands executed the same way, whether we have 1 or n workers. That will help us avoid having multiple ways for command execution.