Fix MetricsServlet initialization (prometheus#739)

Signed-off-by: Fabian Stäber <[email protected]>

Author: fstab

simpleclient_servlet/src/main/java/io/prometheus/client/exporter/MetricsServlet.java

@@ -41,6 +41,7 @@ public MetricsServlet(CollectorRegistry registry, Predicate<String> sampleNameFi
   @Override
   public void init(ServletConfig servletConfig) throws ServletException {
     try {
+      super.init(servletConfig);
       exporter.init(Adapter.wrap(servletConfig));
     } catch (ServletConfigurationException e) {
       throw new ServletException(e);

simpleclient_servlet_jakarta/src/main/java/io/prometheus/client/servlet/jakarta/exporter/MetricsServlet.java

@@ -40,6 +40,7 @@ public MetricsServlet(CollectorRegistry registry, Predicate<String> sampleNameFi
   @Override
   public void init(ServletConfig servletConfig) throws ServletException {
     try {
+      super.init(servletConfig);
       exporter.init(wrap(servletConfig));
     } catch (ServletConfigurationException e) {
       throw new ServletException(e);