Configuring wrappers to use writable copies of paths

[thou-vow]

The idea is for the wrapper to instead of directly using paths pointing to store, copy these paths to a chosen location as writable and use that (of course always check if the aimed file or directory exists in the chosen location before doing that operation). This makes the process of fixing small bits of configuration much quicker, avoiding Nix evaluation/building until everything's done.
I wonder if that's possible without a new implementation of makeWrapper interface.

[BirdeeHub]

So, you can put any path there. Including outside of the store.

So, if that path is there at runtime, it will work, and you will be able to edit it.

However, if it was outside of the store, its not going to copy it there for you.

In order to copy it there, we only have THAT derivation to work with.

The options we can do from here would be:

• Make the wrapper copy it at runtime if it doesnt exist. The noctalia-shell wrapper module does this actually.

• Export a service via one of the paths for that which copies it there somehow on some sort of trigger, then in nixos or home manager install it via systemd.packages option, and then enable the service. This will be much easier when we have dedicated options for generating those service files, which we do not yet, but can already be done with constructFiles or buildCommand options.

• Usually, it is nice to simply change the path to a regular "/home/user/wherever" kind of path when editing and build that on its own and mess with it until you are happy with its behavior, and then change the path back and rebuild with it as part of your configuration using a pure path when done.