[RHDEVDOCS-7037] Add example for triggering pipelines from image registry webhooks

[preetma-redhat]

Summary

• Adds a procedure for starting a PipelineRun from a Red Hat Quay / Quay.io Repository Push webhook, which is the supported way to rebuild when a mirrored registry.redhat.io image is updated.
• Includes TriggerBinding, TriggerTemplate, EventListener, route, Quay notification steps, and a sample curl payload for verification.
• Case: 04322735. Jira: https://redhat.atlassian.net/browse/RHDEVDOCS-7037

Test plan

• Preview the Creating CI/CD solutions for applications using Pipelines assembly and confirm the new Triggering a pipeline from an image registry webhook section renders after Creating webhooks.
• Confirm AsciiDoc attributes ({pipelines-shortname}, {pipelines-title}) resolve and there are no unresolved {registry-redhat-io} placeholders.
• Optional: apply the sample YAML on a cluster with OpenShift Pipelines, expose el-image-push, POST the sample JSON, and check tkn pipelinerun list (requires a rebuild-application-image pipeline or an edited pipelineRef).

Made with Cursor

[openshift-ci]

Hi @preetma-redhat. Thanks for your PR.

I'm waiting for a openshift member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

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