feat: add allowFailure option for workflow steps

[alex-kattathra-johnson]

Fixes #6077

[alex-kattathra-johnson]

@stefreak: Got the errors resolved and the builds successful. Thank you!

[alex-kattathra-johnson]

@stefreak : I've updated the PR based on the discussion from the issue. Could you please do another review when a chance is afforded?

[twelvemo]

Great job on this! I think adding an allowFailure flag on a step is a great idea, however after a longer discussion @stefreak and I figured that in the current format the distinction between onFailure and onError is a bit difficult to understand. This is not due to your implementation, which is great. Some more suggestions on how to proceed in another comment soon.

[stefreak]

@alex-kattathra-johnson Wow, great job, really amazing how you drilled down into the workflow code, and your code looks like it behaves exactly as proposed by @salotz in #6077

During deeper review @twelvemo and me took the time to think again about the user perspective, and while initially I thought adding onFailure is a good idea, it turns out to make workflows harder to explain and workflow code harder to read.

Our proposal is the following:

1. Let's go back to the older version of the PR where you only added allowFailure (And possibly rename that to continueOnError. Let's keep the added tests from the current version 👍
2. Let's open an issue and postpone the onFailure handler to another PR; What we think might be ideal is something like the following, but implementation of that is too complex to shove it into this PR.

kind: Workflow
name: test
steps:
 - name: allowed_to_fail 
   script: this_will_fail
   continueOnError: true
 - if: ${steps.allowed_to_fail.outcome == "error"} 
   script: echo "Step 1 failed, let's clean it up"

[alex-kattathra-johnson]

Sliced the PR with the Occam's razor! 😄

[twelvemo]

Looks good! Thanks for taking the time to rework it again!

[stefreak]

@twelvemo and me made some additional changes to the logging and error handling behaviour. Looks good to go now, if the tests pass