Configure Trigger Scaling with KEDA through annotations

[Cali0707]

Problem
Currently, users can configure KEDA scaling options through annotations when creating a KafkaSource. We should support the same set of annotations on triggers.

Persona:
Which persona is this feature for?

Exit Criteria
Scaling for triggers can be configured through annotations with the same API as KafkaSources

Time Estimate (optional):
How many developer-days do you think this may take to resolve? 1-2

Additional context (optional)
Add any other context about the feature request here.

[Cali0707]

@pierDipi what do you think of allowing users to also set the annotations on the broker? I could see this maybe being easier, rather than needing to set it on each trigger. This would be the following behaviour then:

1. If there is an annotation on the trigger, use those values
2. If there is no annotation on the trigger, but there is an annotation on the broker, use the broker annotation
3. Otherwise, use the default values

[Cali0707]

Also @pierDipi - regarding out discussion about how to set the scale on the trigger manually, what about: if the autoscaling class is set to disabled, then we will use the AutoscalingMinScale annotation?

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