Be more aggressive with stopping services

What does this Merge Request do and why?

This MR aims to be more aggressive when it comes to stopping services when gdk stop is executed to ensure we don't have any zombie processes lying around.

When running gdk stop, for each service runit would execute sv/<service>/control/t which would:

Before

• Kill off the PID group (-<PID>) by sending the -TERM (-15) signal => kill -TERM -<PID>
• Kill off the PID (<PID>) by sending the -TERM (-15) signal => kill -TERM <PID>

For the webpack service however, we'd send -KILL (-9) explicitly, instead of -TERM (-15).

Now

• Kill off the PID group (-<PID>) by sending the -TERM (-15) signal => kill -TERM -<PID>
• Kill off the PID (<PID>) by sending the -TERM (-15) signal => kill -TERM <PID>
• Give the PID up to 3 secs to die off on its own and:
  • If PID dead:
    • Exit with 0
  • If PID not dead:
    • Kill off the PID group (-<PID>) by sending the -KILL (-9) signal - kill -KILL -<PID>
    • Kill off the PID (<PID>) by sending the -KILL (-9) signal - kill -KILL <PID>

Unfortunately after lots of experimentation, webpack still needs to be sent the KILL signal initially, otherwise it goes zombie 😞

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.