Add metadata Servlet

- add new servlet to get meta data from PlantUML diagram
- meta data get not only be requested as text but also as json if you set the `Accept`-header to json
- add `metadata` servlet tests
- GET: like the Proxy where you can pass a URL which the servlet will use to fetch the diagram image
- POST: file upload

pom.xml

@@ -180,6 +180,12 @@
       <version>${junit.version}</version>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-params</artifactId>
+      <version>${junit.version}</version>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>org.junit.platform</groupId>
       <artifactId>junit-platform-suite-api</artifactId>