feat: fix servlet3.0 header capture (#415)

* fix servlet3.0 headeres capture

* fix condition

Author: thugrock7

instrumentation/servlet/servlet-3.0/src/main/java/io/opentelemetry/javaagent/instrumentation/hypertrace/servlet/v3_0/nowrapping/Servlet30AndFilterInstrumentation.java

@@ -183,6 +183,9 @@ public static void exit(
 
         if (!request.isAsyncStarted()) {
           if (instrumentationConfig.httpHeaders().response()) {
+            if (throwable == null && !httpResponse.isCommitted()) {
+              httpResponse.flushBuffer();
+            }
             for (String headerName : httpResponse.getHeaderNames()) {
               String headerValue = httpResponse.getHeader(headerName);
               currentSpan.setAttribute(
@@ -212,6 +215,7 @@ public static void exit(
                 urlEncodedMapContextStore);
           }
         }
+      } catch (IOException e) {
       } finally {
         Throwable tmp = throwable;
         while (tmp != null) { // loop in case our exception is nested (eg. springframework)