chore: add Dockerfile for containerized builds

Dockerfile

@@ -0,0 +1,21 @@
+FROM eclipse-temurin:21-jdk AS build
+WORKDIR /workspace
+
+COPY .mvn/ .mvn/
+COPY mvnw pom.xml ./
+RUN ./mvnw -B -q dependency:go-offline
+
+COPY src/ src/
+RUN ./mvnw -B -q clean package -DskipTests
+
+FROM eclipse-temurin:21-jre AS runtime
+WORKDIR /app
+
+RUN groupadd --system slotline && useradd --system --gid slotline --home /app slotline
+
+COPY --from=build /workspace/target/slotline-0.0.1-SNAPSHOT.jar app.jar
+USER slotline
+
+EXPOSE 8080
+ENV JAVA_OPTS=""
+ENTRYPOINT ["sh", "-c", "exec java $JAVA_OPTS -jar app.jar"]