Support prometheus plugin

Author: Jc2k

Dockerfile

@@ -27,3 +27,6 @@ FROM elasticsearch:5.5.2
 COPY elasticsearch.yml /usr/share/elasticsearch/config/elasticsearch.yml
 COPY --from=builder /src/build/distributions/tinyauth-0.0.1-SNAPSHOT.zip /
 RUN elasticsearch-plugin install file:/tinyauth-0.0.1-SNAPSHOT.zip
+
+COPY elasticsearch-prometheus-exporter-5.5.2.1-SNAPSHOT.zip /
+RUN elasticsearch-plugin install file:/elasticsearch-prometheus-exporter-5.5.2.1-SNAPSHOT.zip