Move lsp config to local file structure

.config/nvim/lsp/nixd.lua

@@ -0,0 +1,15 @@
+---@brief
+---
+--- https://github.com/nix-community/nixd
+---
+--- Nix language server, based on nix libraries.
+---
+--- If you are using Nix with Flakes support, run `nix profile install github:nix-community/nixd` to install.
+--- Check the repository README for more information.
+
+---@type vim.lsp.Config
+return {
+  cmd = { 'nixd' },
+  filetypes = { 'nix' },
+  root_markers = { 'flake.nix', '.git' },
+}