Add Jdk21 build (#316)

* Add Jenkinsfile tailored for JDK21 for ci.jenkins.io

* Require 2.401.3 as minimum Jenkins version

* fix(maven): 3.8.1 required to no longer download dependencies via HTTP (use HTTPS instead).

* fix(maven): Add to use a newer version (3.9.4) to get rid of the error.

* fix(Jenkinsfile): POSIX compliance.

* Updated the parent POM

* Back to the original version for Jenkins and the BOM

* Let's keep the JDK11 for the time being

Jenkinsfile

@@ -1,5 +1,7 @@
-buildPlugin(useContainerAgent: false, configurations: [
-  [ platform: "linux", jdk: "11" ],
-  [ platform: "windows", jdk: "11" ],
-  [ platform: "linux", jdk: "17" ]
+buildPlugin(
+  useContainerAgent: true,
+  configurations: [
+    [platform: "linux", jdk: "11"],
+    [platform: 'linux', jdk: 21],
+    [platform: 'windows', jdk: 17],
 ])