Add attributes for Elasticsearch/Logstash/Kibana images

As requested by @gsmet [here](quarkusio/quarkus#25663 (review)).

See https://github.com/quarkusio/quarkus/pull/25663/files#diff-749f6f9897e14f3c05890960c13ad402b7541d714116175a61cada4e64f085a1R2827-R2829
See https://github.com/quarkusio/quarkus/pull/25663/files#diff-150bdf617c2dc80dc5a9d5f1313f44a73950a96ca7b166b79a35b15f4c84f193R79-R82

Author: yrodiere

_guides/attributes.adoc

@@ -10,6 +10,9 @@
 :surefire-version: 3.0.0-M5
 :restassured-version: 4.5.1
 :gradle-version: 7.4.2
+:elasticsearch-image: docker.io/elastic/elasticsearch:7.16.3
+:logstash-image: docker.io/elastic/logstash:7.16.3
+:kibana-image: docker.io/elastic/kibana:7.16.3
 :jandex-maven-plugin-version: 1.2.2
 
 :generated-dir: ../_generated-config/latest