This adds the `nixvimExtend` attribute to the generated standalone
derivation, this attribute takes a module as an argument and returns a
new standalone derivation with the initial module & the extended module
merged together.
* plugin/committia: Use correct maintainers import
* plugins/neocord: Remove redyf as the entry is not in the list
* docs: Allow to add an URL to the plugin
This requires pulling quite a lot of code from nixpkgs in order to
make the `either` type work correctly, the effects can be seen for
example in the documentation of `ollama.promps` and `ollama.actions`
