Add Docker support and update Java version to 21

Dockerfile

@@ -0,0 +1,22 @@
+FROM maven:3-amazoncorretto-21-alpine AS builder
+WORKDIR /workspace
+
+COPY pom.xml ./
+COPY mvnw ./
+COPY .mvn .mvn
+
+RUN mvn -B -DskipTests dependency:go-offline
+
+COPY src ./src
+RUN mvn -B -DskipTests package
+
+FROM amazoncorretto:21-alpine AS runtime
+WORKDIR /app
+
+COPY --from=builder /workspace/target/*.jar /app/app.jar
+
+ENV JAVA_OPTS="-XX:MaxRAMPercentage=75.0 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/tmp -Djava.security.egd=file:/dev/./urandom"
+
+EXPOSE 8080
+
+ENTRYPOINT ["sh", "-c", "exec java $JAVA_OPTS -jar /app/app.jar"]