Sync with Elasticsearch main branch (#171)

This PR introduces changes aligned with Elasticsearch main branch which a big change, JDK 21 requirement.

* Update JDK to 21.
* Fix failed unit test.

Author: mashhurs

.java-version

@@ -1 +1 @@
-17.0
+21.0

build.gradle

@@ -33,8 +33,8 @@ description                = "Elastic Integration filter"
 // ===========================================================================
 
 java {
-    sourceCompatibility = 17
-    targetCompatibility = 17
+    sourceCompatibility = 21
+    targetCompatibility = 21
 }
 tasks.withType(JavaCompile) {
     options.encoding = 'UTF-8'

lib/logstash/filters/elastic_integration.rb

@@ -105,7 +105,7 @@ class LogStash::Filters::ElasticIntegration < LogStash::Filters::Base
   # is not encumbered by those dependencies.
   def initialize(*a, &b)
     ensure_complete_logstash!
-    ensure_java_major_version!(17)
+    ensure_java_major_version!(21)
 
     require_relative "elastic_integration/jar_dependencies"
     require_relative "elastic_integration/event_api_bridge"

spec/unit/elastic_integration_spec.rb

@@ -31,7 +31,7 @@
 
       it 'prevents initialization and presents helpful guidancee' do
         expect { described_class.new({}) }.to raise_error(LogStash::EnvironmentError)
-                                                .with_message(including("requires Java 17 or later", # reason +
+                                                .with_message(including("requires Java 21 or later", # reason +
                                                                         "current JVM version `11.0.16.1`",
                                                                         "remove the plugin", # guidance options
                                                                         "run Logstash with a supported JVM."))