fix: Admission Webhook blocks ScaledObject without metricType with fallback

[rickbrouwer]

In scaler.go there is a function GetMetricTargetType which helps get the metric target type of the scaler. If no metric type is provided then the AverageValue is used.

In v2.17 is a check in the webhook admission that if at least one trigger is of the type AverageValue, then having fallback is valid. A metricType is optional and often not supplied. As a result, many scaledObjects now give errors when supplying a fallback without metricType.

Adding an extra check if the trigger.MetricType is empty will fix this issue. This check is also in the scaler.go.

Any feedback regarding the chosen solution is okay.

Checklist

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Fixes #6696

[wozniakjan]

thank you!

could you please also add an e2e test for this case so future KEDA releases are a bit safer? Don't feel pressured, if it's not in your capacity at the moment, I'm happy to approve this as is and add the e2e test coverage later this week.

[wozniakjan]

/run-e2e fallback|scaling_modifiers
Update: You can check the progress here

[rickbrouwer]

thank you!

could you please also add an e2e test for this case so future KEDA releases are a bit safer? Don't feel pressured, if it's not in your capacity at the moment, I'm happy to approve this as is and add the e2e test coverage later this week.

I'll add a unit test first. That also does a good check. I saw that scaledobject_types doesn't have this anyway, so here it is :)

I will create a test case in the e2e of fallback later.

[rickbrouwer]

Also added an e2e test

[wozniakjan]

/run-e2e fallback|scaling_modifiers
Update: You can check the progress here

[rickbrouwer]

Added more unit tests for the remaining functions of scaledobject_types

[wozniakjan]

/run-e2e fallback|scaling_modifiers
Update: You can check the progress here

[wozniakjan]

/run-e2e fallback|scaling_modifiers
Update: You can check the progress here

[zroubalik]

LGTM, thanks!