Add missing required property to docs

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+label: docsite_pr

lib/ansible/modules/network/aci/aci_aaa_user_certificate.py

@@ -29,6 +29,7 @@ options:
   aaa_user:
     description:
     - The name of the user to add a certificate to.
+    required: yes
   aaa_user_type:
     description:
     - Whether this is a normal user or an appuser.