mgr/prometheus: replace whitespaces in metrics' names

Fixes: https://tracker.ceph.com/issues/39434

Signed-off-by: Alfonso Martínez <almartin@redhat.com>
(cherry picked from commit 843802f)

src/pybind/mgr/prometheus/module.py

@@ -121,7 +121,7 @@ def str_expfmt(self):
         def promethize(path):
             ''' replace illegal metric name characters '''
             result = path.replace('.', '_').replace(
-                '+', '_plus').replace('::', '_')
+                '+', '_plus').replace('::', '_').replace(' ', '_')
 
             # Hyphens usually turn into underscores, unless they are
             # trailing