[release-1.16] Backport of knative-extensions/kn-plugin-event#375

[cardil]

release-1.16

Backport of knative-extensions#375

Requires openshift-knative/client#504

[cardil]

This is failing each time, seen also on other PRs vs release-1.16 (#545):

=== RUN   TestInClusterSender/KnativeService/Setup/Deploy_KnService
=== PAUSE TestInClusterSender/KnativeService/Setup/Deploy_KnService
=== CONT  TestInClusterSender/KnativeService/Setup/Deploy_KnService
    kn_service.go:144: admission webhook "validation.webhook.serving.knative.dev" denied the request: validation failed: invalid value: .config/wathola: spec.template.spec.containers[0].volumeMounts[0].mountPath
--- FAIL: TestInClusterSender/KnativeService/Setup/Deploy_KnService (0.02s)

This happens only on Openshift, upstream is good. I need to debug root cause.

[cardil]

#557 should fix the test failure in this PR

[dsimansk]

/approve
/lgtm

[openshift-ci]

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