feat: Allow retry strategy on non-leaf nodes, eg for step groups. Fixes #1891

[markterm]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR is (a) conventional, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234". Why? for the release notes.
• Optional. I've added My organization is added to the README.
• I've signed the CLA and required builds are green.

Fixes #1891

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@cdbc619). Click here to learn what that means.
The diff coverage is 72.22%.

@@            Coverage Diff            @@
##             master    #1892   +/-   ##
=========================================
  Coverage          ?   11.43%           
=========================================
  Files             ?       71           
  Lines             ?    27903           
  Branches          ?        0           
=========================================
  Hits              ?     3192           
  Misses            ?    24305           
  Partials          ?      406

Impacted Files	Coverage Δ
workflow/validate/validate.go	74.57% <ø> (ø)
workflow/controller/operator.go	60.57% <72.22%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cdbc619...a4f72b2. Read the comment docs.

[alexec]

It's looking pretty good at the moment. Could you please look into writing some tests?

[markterm]

Sure - are there any specific scenarios you're thinking of other than the one I already created?

[alexec]

@jessesuen do you want to review this one? Or at least provide commentary on the impact on removing this constraint?

[alexec]

@mark9white I've tried to fix the conflict - but I think I've failed to do a good job - if you still want this - do you want to take a look?

[markterm]

@alexec I've fixed the conflict