Fix the annotating for snapshot and staging (#39299)

* Fix the annotating for snapshot and staging

This commit adds the `--append` flag to the buildkite-annotate so that
when it is called by the snapshot and staging steps, it will not overwrite
the other annotation.

Signed-off-by: Alexandros Sapranidis <alexandros@elastic.co>

.buildkite/scripts/dra.sh

@@ -88,5 +88,5 @@ if [[ "$DRY_RUN" != "--dry-run" ]]; then
   rm rm-output.txt
 
   # and make it easily clickable as a Builkite annotation
-  printf "**Summary link:** [${SUMMARY_URL}](${SUMMARY_URL})\n" | buildkite-agent annotate --style=success 
+  printf "**${DRA_WORKFLOW} summary link:** [${SUMMARY_URL}](${SUMMARY_URL})\n" | buildkite-agent annotate --style=success --append
 fi