Doc: Fix incorrect usage of \generatelist

The \generatelist command takes an optional argument
that affect how the members are listed, for example,
`classesbymodule` which creates an annotated list of
the classes in a named C++ module.

`groupsbymodule` is not recognized or documented. QDoc
falls back to generating a list of all members of a
group in this case. While the end result is correct,
this relies on an undocumented feature that is likely
to change and break.

Replace these instances with an explicit \annotatedlist
command that produces the same output.

Task-number: QTBUG-138901
Change-Id: I4c36087ff39efc740bc938888aa2531f635d9b67
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
(cherry picked from commit 1cc23b20ef)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/mqtt/doc/src/index.qdoc

@@ -59,5 +59,5 @@
     In addition, it is available under the
     \l{GNU General Public License, version 3}.
 
-    \generatelist{groupsbymodule attributions-qtmqtt}
+    \annotatedlist attributions-qtmqtt
 */