Add retry feature

[birdayz]

Make commands retryable:

...
tasks:
  build:
    retry:
      attempts: 3
      exit_codes:
        - 1
        - 127
    cmds:
     ...

If exit_codes is provided, only the provided exit codes are retryable. otherwise, all exit code are retried.

I have a use case, where a task runs many other tasks via deps. One of them fails, it all fails. In the end, CI retrys the entire task invocation, which will again run all of these parallel tasks. However, it would be much better to only retry the individual task that fails.
I can do the retry within the cmd, but that's not very elegant and re-usable i feel.

[danilobuerger]

Best case, this should also include a delay.