Core version bump to 9.1.0 (elastic#16991)

Author: mashhurs

versions.yml

@@ -1,7 +1,7 @@
 ---
 # alpha and beta qualifiers are now added via VERSION_QUALIFIER environment var
-logstash: 9.0.0
-logstash-core: 9.0.0
+logstash: 9.1.0
+logstash-core: 9.1.0
 logstash-core-plugin-api: 2.1.16
 
 bundled_jdk: