Match Common Name attribute in Subject

ipa cert_find command has an option called --subject.
The option is documented as --subject=STR Subject.
It is expected that a --subject option searches by X.509 subject field but it does not do so.
It searches for CN not cert subject. Hence changing content of --subject help option.

Resolves: https://pagure.io/freeipa/issue/7322
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

ipaserver/plugins/cert.py

@@ -1307,7 +1307,7 @@ class cert_find(Search, CertMethod):
     takes_options = (
         Str('subject?',
             label=_('Subject'),
-            doc=_('Subject'),
+            doc=_('Match cn attribute in subject'),
             autofill=False,
         ),
         Int('min_serial_number?',