Initial set of files defined in hjem

[Delamox]

Hi there, while working on my configuration I discovered that there wasn't really a way to put an initial user-editable set of files into a home folder, something I thought would be a good hjem feature.

I am trying to create a multi user (think 10-20) configuration for a research project into deploying nix into a classroom at my school. And while I have managed to achieve an easy way to define files unable to be edited by these users using hjem, I have been unable to find a way to provide an initial 'default' set of files able to be customized by the user (not linked to the store) after initial placement into their home folders.

Optionally it would also be able to 'update' said initial files to new versions as long as they have not been edited by the user, but this would likely be impossible to properly implement since that would be impure.

[eclairevoyant]

We'll expose ignore_modification, which would be used in conjunction with type = "copy", but this will also require support from smfh if you want to link an entire dir over. I'll link a PR and update with an example once that first part is taken care of, in any case.