Fail Fast control for with item task

[exp-vkishore]

Currently the incomplete items in a task's with list won't be processed if there are no active task item and parent task has failed status. For example let's consider this workflow

version: 1.0

description: A workflow demonstrating with items and concurrent processing.

input:
  - members  # [0,1,2,3]
  - concurrency: 1

tasks:
  task1:
    with:
      items: <% ctx(members) %>
      concurrency: <% ctx(concurrency) %>
    action: core.local cmd="[ item() -eq  1 ] && exit 1 || exit 0"

If we run above workflow it will process items 0 and 1 only, as on member 1 action will fail which will set the task1 status as fail and the concurrency is set to 1 there for there will be no active task item and state of task1 will be set to failed from running.
And no other item will be processed.

With this change I have introduce a boolean parameter failfast in task which will decide wether to fail the entire task if there are not active task item and task status is failed.

version: 1.0

description: A workflow demonstrating with items and concurrent processing.

input:
  - members  # [0,1,2,3]
  - concurrency: 1

tasks:
  task1:
    failfast: false
    with:
      items: <% ctx(members) %>
      concurrency: <% ctx(concurrency) %>
    action: core.local cmd="[ item() -eq  1 ] && exit 1 || exit 0"

[cognifloyd]

Ooh. I really like ux for this!

Please add some tests so we can move this forward.

I believe this will address StackStorm/st2#4968

Something like this was requested in StackStorm/st2#5054 (comment) The rest of that issue discusses failfast across parallel workflow branches. This PR only addresses the piece mentioned in that comment: failfast for with items loops.

And though this is slightly orthogonal, I think this PR may be part of the solution for StackStorm/st2#4679

[cognifloyd]

Please drop the whitespace only changes. Use black to reformat.

[m4dcoder]

Changes to the workflow definition language should start as an issue with the proposal otherwise you are going to expect rework. Having said this, I have some issue with the proposal here.

• As I understand the case here, failfast is used to control flow for with items. The attribute should be defined under the with models at https://docs.stackstorm.com/orquesta/languages/orquesta.html#with-items-model.
• So far, the workflow definition language has avoided hard coding success and failure in the language. I like to keep it that way where possible. Can we do something like flow: stopOnFail and flow: continueOnFail? The flow: stopOnFail should be the default when it is not specified to be consistent with existing behavior.

[cognifloyd]

@exp-vkishore would you be able to revisit this? What do you think of @m4dcoder 's suggestion of a flow: keyword under with:?

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