fix: apply fallback in polling loop to enable scaling from zero

[rickbrouwer]

When a ScaledObject is scaled to zero and the scaler encounters an error, the fallback mechanism is only triggered during HPA metric requests via GetScaledObjectMetrics, but not during the polling loop in getScaledObjectState. This caused the ScaledObject to remain at zero replicas indefinitely when errors occurred, as the polling loop would continuously fail without activating the fallback, preventing HPA from ever being consulted.

Fallback now works in both, HPA requests and polling interval checks.

The only question I have is whether it's by design that it doesn't switch to Fallback with 0 replicas, but I can't think of that myself. Please consider this when considering whether this was a deliberate choice. If not, I believe this PR resolves the issue.

Some extra new info;

It turned out to be a more change than I anticipated. I initially thought I'd add a simple fallback to getScalerState, but it turned out that scalingModifiers started having issues.
Therefore, I had to make some further adjustments to ensure the fallback worked properly from all positions.

Checklist

• I have verified that my change is according to the deprecations & breaking changes policy
• Tests have been added
• Changelog has been updated and is aligned with our changelog requirements
• Commits are signed with Developer Certificate of Origin (DCO - learn more)

Fixes #7239

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[rickbrouwer]

/run-e2e internals
Update: You can check the progress here

[rickbrouwer]

/run-e2e internals
Update: You can check the progress here

[rickbrouwer]

/run-e2e internals
Update: You can check the progress here

[rickbrouwer]

/run-e2e internals
Update: You can check the progress here

[rickbrouwer]

/run-e2e internals
Update: You can check the progress here

[rickbrouwer]

/run-e2e internals
Update: You can check the progress here

[rickbrouwer]

/run-e2e internals
Update: You can check the progress here

[rickbrouwer]

/run-e2e internals
Update: You can check the progress here

[rickbrouwer]

/run-e2e internals
Update: You can check the progress here