erp5_base: MailMessage_sendByActivy can be retried

As since the introduction of Internet Message Post it is more likely that
conflicts happen. Also, this operation is now safe as sending email in
Entity_sendEmail is made transactionally (as the interaction with MailHost
is done through the creation of an activity)

bt5/erp5_base/SkinTemplateItem/portal_skins/erp5_base/MailMessage_sendByActivity.py

-# We do not want to retry those activities, as sending email is not transactional safe
-activate_kw = kw.pop('activate_kw', {})
-activate_kw['max_retry'] = 0
-activate_kw['conflict_retry'] = False
 
 context.getPortalObject().portal_catalog.searchAndActivate(
   method_id="Entity_sendEmail",
   destination_related_uid=context.getUid(),
   method_kw=method_kw,
-  activate_kw=activate_kw,
+  activate_kw=kw.pop('activate_kw', {}),
   **kw)