Update dummy-subscriber to use PubsubMsg struct

[JaydipGabani]

After the current PR for pub-sub #2538 is merged, let's update the dummy-subscriber to import PubsubMsg struct from audit

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[ritazh]

@JaydipGabani should this be closed?

[JaydipGabani]

@ritazh I was waiting on Max's PR on controller-runtime to merge. Otherwise adding gatekeeper as a dependency in go.mod creates error at build time with undefined: cache.InformerGetOption error.

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.