Dynamically generate version for container invocation

Co-authored-by: Ry Biesemeyer <[email protected]>

Author: donoghuc

.buildkite/pull_request_pipeline.yml

@@ -138,7 +138,8 @@ steps:
       set -euo pipefail
       source .buildkite/scripts/common/vm-agent.sh
       ./gradlew --stacktrace artifactDockerObservabilitySRE
-      docker run docker.elastic.co/logstash/logstash-observability-sre:8.19.0-SNAPSHOT \
+      logstash_version="$(awk -F':' '{ if ("logstash" == $1) { gsub(/ /,"",$2); print $2; exit } }' versions.yml)-SNAPSHOT"
+      docker run docker.elastic.co/logstash/logstash-observability-sre:${logstash_version} \
         logstash -e 'input { generator { count => 3 } } output { stdout { codec => rubydebug } }'
 
   - label: ":lab_coat: Integration Tests - FIPS mode / part 1"