Special caller* tags should be available in templates as well

Description

When using a hook we can use %callerDN% to get the dn of the user doing the action. We can also use callerCN, callerUID, callerSN and callerGIVENNAME. See https://docs.fusiondirectory.org/en/documentation/how_to/use/hooks?s[]=callerdn#special-variables

These should be available for templates as well as it might be usefull.

Actual behavior

No access to caller* special vars in templates patterns

Expected behavior

Being able to use %callerDN% is a template

Step by step description of new behaviour

1. Put %callerDN% in a template field
2. Use the template
3. It gets the DN of the caller

Benefits

Possible Drawbacks

Applicable Issues

Put the creator of the group in the group by putting %callerDN% in the member field

Set as description «Created by %callerCN%»