erp5_interface_post: add Manager proxy role on Event_createPostMessage

Otherwise security should be set on Mail Message so Event_createPostMessage can modify them (to add the post as aggregate). This is annoying as mails are usually sent by Entity_sendEmail, which already has a Manager proxy role to allow to easily send Mail Messages to user without creating the related security.

bt5/erp5_interface_post/SkinTemplateItem/portal_skins/erp5_interface_post/Event_createPostMessage.xml

@@ -52,6 +52,14 @@
             <key> <string>_params</string> </key>
             <value> <string>post_portal_type, post_message_data, **kw</string> </value>
         </item>
+        <item>
+            <key> <string>_proxy_roles</string> </key>
+            <value>
+              <tuple>
+                <string>Manager</string>
+              </tuple>
+            </value>
+        </item>
         <item>
             <key> <string>id</string> </key>
             <value> <string>Event_createPostMessage</string> </value>