Add loops walkthrough (with_item/with_param, fanout/fanin)

[elliotgunton]

Pull Request Checklist

• Part of "Getting Started" docs #627
• Tests added Docs only
• Documentation/examples added
• Good commit messages and/or PR title

[flaviuvadan]

I think things like "{{item.name}}" are set automatically for Task arguments. Should we expose that to Step as well?

[codecov]

Codecov Report

Merging #660 (00dc608) into main (7a584be) will decrease coverage by 0.3%.
The diff coverage is n/a.

❗ Current head 00dc608 differs from pull request most recent head 85ddd42. Consider uploading reports for the commit 85ddd42 to get more accurate results

@@           Coverage Diff           @@
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- Coverage   74.6%   74.3%   -0.3%     
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  Lines       3017    3017             
  Branches     575     575             
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- Hits        2252    2244      -8     
- Misses       591     602     +11     
+ Partials     174     171      -3     

see 1 file with indirect coverage changes

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[flaviuvadan]

I think things like "{{item.name}}" are set automatically for Task arguments. Should we expose that to Step as well?

@elliotgunton can confirm these are set automatically for tasks based on arguments inference. So, Task invocation does not need the arguments field when with_param is passed, or with_item, but Step does for now. We should add the same logic to Step as well: https://github.com/argoproj-labs/hera/blob/main/src/hera/workflows/_mixins.py#L469 Motivation here is to not confuse users with these differences of "sometimes I can set a thing on Task but not on Step"

[elliotgunton]

We should add the same logic to Step as well

@flaviuvadan 100% agree - we made this change in the source-kwargs branch here https://github.com/argoproj-labs/hera/blob/d0f117f82616c00592346932fcfcc7c9e0d57677/src/hera/workflows/_mixins.py#LL468C27-L468C27, think it's fine to move it out of the Task try branch in the same way