WIP: Add support for setting Templates in Postorius
This merge request adds support for setting templates in Postorius. Funtionally, this is not a Full Implementation, however, this is working.
This supports Creating Tempaltes for Lists and Domain. It updates Core whenever a template is created or Updated.
However, the functionality for Core to Fetch a template isn't yet implemented and just raises a 404 error.
Requires fixing tapes.