feat(promotion): add ignoreMissingValueFiles to helm-template step

[ksawerykarwacki]

Summary

• Adds ignoreMissingValueFiles boolean option to the helm-template promotion step
• When enabled, missing value files are silently skipped instead of causing an error
• Eliminates the need for empty placeholder YAML files per stage

Closes #4349

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[krancour]

I'm not specifically opposed to this, but I do vaguely recall some prior discussion about this, or else it was a very similar conversation. Whether it was on this exact topic or just similar one, I think @hiddeco may have once expressed some reluctance to the idea of steps that wrap a tool (like helm) having options that the tool itself lacks.

helm template cannot do this.

It is quite possible I am mis-remembering the aforementioned conversation, so let's have @hiddeco weigh in.

fwiw, there is another way to do this in v1.9.0. There's a step that merges a list of YAML files and it already has an option to ignore any that are missing. It would be possible to use that first to merge your YAML files (from most general to most specific) and then use helm template on the one resulting file.

[ksawerykarwacki]

I missed that there is new step for merging YAML (i see that it has this flag implemented).

My reasoning was to bring Kargo on par with ArgoCD, as some folks (including myself) run mix of both (e.g. ArgoCD managed apps for dev, PoCs, etc. and rendered manifests via Kargo for staging and prod). Of course I can wrap yaml-merge and helm-template under single promotion task my-helm-template to achieve the same but will flesh out other limitations (vars only support strings so you cannot pass list of value files to it) and will make things more convoluted just for sake of keeping the action as limited as the original source of inspiration (helm template command)

@hiddeco it is your call then if it is worth to have this or not

[hiddeco]

My concern with a flag at a global level like this is that it opens the gates for incidents where e.g. a typo results in something to go unnoticed because any path is allowed to be missing.

I would be more open to the idea of allowing specific paths to be optional. But the problem with this (and the current API) is that the list of values files is just a simple list (and you can't add fields per list item).

[hiddeco]

I do believe we had the same discussion for the yaml-merge step though, and as it was added at a global level there my concern isn't particularly strong if we follow our own existing API patterns.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.51%. Comparing base (7febfe1) to head (1e69576).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5522   +/-   ##
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  Coverage   55.51%   55.51%           
=======================================
  Files         429      429           
  Lines       31954    31957    +3     
=======================================
+ Hits        17738    17741    +3     
  Misses      13208    13208           
  Partials     1008     1008           

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