change Dockerfile for kontor-spring to multistage and add kontor-javalin

kontor-spring/Dockerfile

@@ -1,5 +1,23 @@
-FROM alpine/java:21-jdk
+# ----------------------------------------------------------------------- #
+FROM gradle:8.7-jdk AS builder
 WORKDIR /
-ADD build/libs/kontor-spring-0.2.0-SNAPSHOT.jar app.jar
-EXPOSE 8000
+COPY ./src/main/ ./src/main/
+COPY ./frontend/ ./frontend/
+COPY ./build.gradle ./
+COPY ./gradle.properties ./
+COPY ./settings.gradle ./
+COPY ./gradle/libs.versions.toml ./gradle/
+RUN gradle bootJar --no-daemon
+
+# ----------------------------------------------------------------------- #
+FROM alpine/java:21-jdk AS run
+
+RUN adduser --system appuser
+USER appuser
+
+COPY --from=builder --chown=appuser:appuser /build/libs/kontor-spring-0.2.0-SNAPSHOT.jar app.jar
+
+EXPOSE 8100
+USER appuser
 CMD ["java", "-jar", "-Dspring.profiles.active=prod", "-Dvaadin.productionMode=true", "app.jar"]
+