nixos/*: add trivial defaultText to options where applicable

[pennae]

"trivial" here means "can just copy the expression, add quotes and it's useful". this mostly means that the default expressions given don't use shortcuts like the ubiquitous cfg = config.${our module name}, runs data through a function not in the default expression, or just anything that can't be read in isolation without knowing the context.

working towards caching most of the option documentation to improve build times. this change might speed up the build a little already, but further changes that improve this even more are upcoming.

we have a good few more commits that add defaultTexts to the remaining options that use cfg shortcuts in their defaults or more complicated expressions, will open a PR with those once this is merged (unless there's wishes to include those changes here). after that we'll probably have some more changes (based on #147265) that make most of the option docs for nixos/modules cacheable.

one commit per module by request of @samueldr :)

[samueldr]

Note that I originally suggested per-module commits for modules with non-trivial changes (which would include the trivial changes for said module too). For trivial only changes, maybe some grouping in bite-sized chunks.

I did also say that if it was my opinion only, I would do it just like this was done now, so I don't mind personally, I only know other contributors, maintainers and devs don't like a flood of discrete commits :).

[ckiee]

I looked at all the diffs and checked the more odd ones out in my local build of the manual. Just one~

Edit: Usually the commit messages for stuff like this are prefixed with treewide:, not nixos/*:.

[roberth]

Please merge when ofborg is successful. 🚀

[pennae]

Please merge when ofborg is successful. 🚀

we don't have commit permissions, so someone else will have to :D

[jtojnar]

Usually the commit messages for stuff like this are prefixed with treewide:, not nixos/*:.

Note that we also have a style rule that NixOS changes should be prefixed by nixos/: https://nixos.org/manual/nixpkgs/stable/#submitting-changes-making-patches

[ckiee]

Note that we also have a style rule that NixOS changes should be prefixed by nixos/: https://nixos.org/manual/nixpkgs/stable/#submitting-changes-making-patches

Mhm, so a treewide NixOS change is kind of undefined behavior. I've created a (probably naive) PR to fix that: #148996