[WIP] Use and test KafkaSource v1 API

[pierDipi]

Replace usages of v1beta1 KafkaSource to v1 KafkaSource

Part of #3953

[knative-prow]

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[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 45.51%. Comparing base (6235e66) to head (243538b).

Files with missing lines	Patch %	Lines
...rnalskafkaeventing/v1alpha1/consumer_validation.go	0.00%	2 Missing ⚠️
control-plane/pkg/autoscaler/keda/keda.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4138      +/-   ##
==========================================
- Coverage   45.53%   45.51%   -0.02%     
==========================================
  Files         270      270              
  Lines       19925    19925              
==========================================
- Hits         9072     9069       -3     
- Misses      10127    10129       +2     
- Partials      726      727       +1     

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[pierDipi]

/retest-required

[pierDipi]

This can be merged only after 1.16 is out

[pierDipi]

/retest