`config` is a loaded term within modules and options.
`settings` is the name usually used for freeform config in nixvim and
most other module configurations.
Convert the `attrsOf (servers.nix)` option to a freeform submodule.
Declare a `servers.nix` option for each lsp server listed in
`lsp-packages.nix` that has a known nixpkgs package.
This allows users to override the name used for a given `lsp.servers.*`
entry. The default is still the attr-name.
This may be useful to inject raw lua, or to configure the same server in
different ways via different attrs.
