RSPEED-3082: add build-nudge-files annotation for cross-repo nudging

The default nudge file pattern (.*Dockerfile.*, .*.yaml, .*Containerfile.*)
does not match .yml files. Since lscore-deploy uses
openshift/lightspeed-stack.yml, the nudge controller silently skips it.

This annotation explicitly targets the correct file so the nudge controller
can find and update the image digest reference after each push build.

Signed-off-by: Ellis Low <elow@redhat.com>

Author: Lifto

.tekton/lightspeed-stack-push.yaml

@@ -2,6 +2,7 @@ apiVersion: tekton.dev/v1
 kind: PipelineRun
 metadata:
   annotations:
+    build.appstudio.openshift.io/build-nudge-files: "openshift/lightspeed-stack.yml"
     build.appstudio.openshift.io/repo: https://github.com/lightspeed-core/lightspeed-stack?rev={{revision}}
     build.appstudio.redhat.com/commit_sha: '{{revision}}'
     build.appstudio.redhat.com/target_branch: '{{target_branch}}'