added docker support

Dockerfile

@@ -0,0 +1,18 @@
+FROM alpine as mvn
+
+RUN apk add maven
+
+
+FROM mvn as builder
+
+WORKDIR /build
+ADD . .
+RUN mvn package
+
+
+FROM eclipse-temurin:17-jdk-alpine
+
+WORKDIR /backend
+COPY --from=builder /build/target/swa-jodel-backend.jar .
+
+ENTRYPOINT ["java","-jar","/backend/swa-jodel-backend.jar"]