Design and implement batch publishing for pub-sub

[JaydipGabani]

Describe the solution you'd like
Right now Pubsub interface only supports the publishing of individual events. Add logic and functionality to support batch publishing as well since many of the providers support batch publishing.

Anything else you would like to add:
Initial pubsub feature is added in #2538

Environment:

• Gatekeeper version:
• Kubernetes version: (use kubectl version):

[stale]

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.

[maxsmythe]

going concern

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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.