Introduce multistage Docker build for optimized image size

Implemented a multistage Docker build, separating build and runtime stages to reduce the final image size and improve security. Adjusted `.dockerignore` to exclude unnecessary files from the build context and updated the base JRE image to use the build output efficiently.

.dockerignore

@@ -1,15 +1,8 @@
 .git
 .github
 .idea
-.mvn
-src
 classes
 logs
-target/*
-!target/netneutrality.jar
+target
 *.iml
 README.md
-checkstyle.xml
-mvnw
-mvnw.cmd
-pom.xml