Sandman: Add a button to edit local/custom templates

[bastik-1001]

Is your feature request related to a problem or use case?

Local custom templates can be edited by double-clicking on them, which is not indicated by the UI, so on-top of being able to double-clicking it, make it possible by clicking a button.

Describe the solution you'd like

Having a button, possibly labeled "Edit" (allows it to be re-used elsewhere) or "Edit entry" (still vague enough to re-use it) or "Edit template" (makes clear what is being edited).

Describe alternatives you've considered

Other ways to make clear, that local templates can be edited or how to edit them are still not off the table.

The experience for other elements, where there are entries that can be edited are different, as they are edited in the exact same window and show the rules in that window, the templates could simply be misunderstood as a mere list.