Add Spring Boot Twitch overlay server with CI and Docker

Dockerfile

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+FROM maven:3.9-eclipse-temurin-17 AS build
+WORKDIR /app
+COPY pom.xml ./
+RUN mvn -B dependency:go-offline
+COPY src ./src
+RUN mvn -B package -DskipTests
+
+FROM eclipse-temurin:17-jre
+WORKDIR /app
+COPY --from=build /app/target/imgfloat-0.0.1-SNAPSHOT.jar app.jar
+EXPOSE 8080 8443
+ENV JAVA_OPTS=""
+ENTRYPOINT ["sh", "-c", "java $$JAVA_OPTS -jar app.jar"]