[WIP] Use and test KafkaSource v1 API

[pierDipi]

Replace usages of v1beta1 KafkaSource to v1 KafkaSource

Part of #3953

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: pierDipi

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[knative-prow]

@pierDipi: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
unit-tests_eventing-kafka-broker_main	09908e5	link	true	/test unit-tests
build-tests_eventing-kafka-broker_main	09908e5	link	true	/test build-tests
upgrade-tests_eventing-kafka-broker_main	09908e5	link	true	/test upgrade-tests
channel-integration-tests-ssl_eventing-kafka-broker_main	09908e5	link	true	/test channel-integration-tests-ssl
reconciler-tests-keda_eventing-kafka-broker_main	09908e5	link	true	/test reconciler-tests-keda
channel-integration-tests-sasl-plain_eventing-kafka-broker_main	09908e5	link	true	/test channel-integration-tests-sasl-plain
integration-tests_eventing-kafka-broker_main	09908e5	link	true	/test integration-tests
channel-integration-tests-sasl-ssl_eventing-kafka-broker_main	09908e5	link	true	/test channel-integration-tests-sasl-ssl
reconciler-tests_eventing-kafka-broker_main	09908e5	link	true	/test reconciler-tests
reconciler-tests-namespaced-broker_eventing-kafka-broker_main	09908e5	link	true	/test reconciler-tests-namespaced-broker
channel-reconciler-tests-sasl-plain_eventing-kafka-broker_main	09908e5	link	true	/test channel-reconciler-tests-sasl-plain
channel-reconciler-tests-sasl-ssl_eventing-kafka-broker_main	09908e5	link	true	/test channel-reconciler-tests-sasl-ssl
channel-reconciler-tests-ssl_eventing-kafka-broker_main	09908e5	link	true	/test channel-reconciler-tests-ssl

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