[rest] special handling for StreamingOutput (#4145)

Signed-off-by: Jörg Sautter <[email protected]>

Author: joerg1985

Diff for: bundles/org.openhab.core.io.rest.core/src/main/java/org/openhab/core/io/rest/core/internal/GsonMessageBodyWriter.java

@@ -23,6 +23,7 @@
 import javax.ws.rs.core.MediaType;
 import javax.ws.rs.core.MultivaluedMap;
 import javax.ws.rs.core.Response.ResponseBuilder;
+import javax.ws.rs.core.StreamingOutput;
 import javax.ws.rs.ext.MessageBodyWriter;
 
 import org.openhab.core.io.rest.JSONInputStream;
@@ -81,6 +82,8 @@ public void writeTo(final T object, final Class<?> type, final Type genericType,
         try {
             if (object instanceof InputStream stream && object instanceof JSONInputStream) {
                 stream.transferTo(entityStream);
+            } else if (object instanceof StreamingOutput streaming) {
+                streaming.write(entityStream);
             } else {
                 entityStream.write(gson.toJson(object).getBytes(StandardCharsets.UTF_8));
             }