Add ".vtx" as a recognized extension for ADIOS2VTXReader

Remoting/Application/Resources/proxies_adios2_vtx.xml

@@ -32,7 +32,7 @@
       <Hints>
         <ReaderFactory extensions="bp"
                        file_description="VTX reader: ADIOS2 BP3 File" />
-        <ReaderFactory extensions="bp bp4"
+        <ReaderFactory extensions="bp bp4 vtx"
                        is_directory="1"
                        file_description="VTX reader: ADIOS2 BP4 Directory" />
       </Hints>