Ability for non-sudo admins to create their own templates

[wavy-cat]

Currently, all templates are shared among all admins, and non-sudo admins cannot create their own.
If an admin needs a personal template, they have to ask a sudo admin to create it.

To solve this, please add template ownership and allow non-sudo admins to create their own templates.
It might also be useful to let sudo admins create public templates.

This idea aligns well with #61 about separating group access for non-sudo admins. I think this should be implemented together.