Move lsp config to local file structure

.config/nvim/lsp/rnix.lua

@@ -0,0 +1,20 @@
+---@brief
+---
+--- https://github.com/nix-community/rnix-lsp
+---
+--- A language server for Nix providing basic completion and formatting via nixpkgs-fmt.
+---
+--- To install manually, run `cargo install rnix-lsp`. If you are using nix, rnix-lsp is in nixpkgs.
+---
+--- This server accepts configuration via the `settings` key.
+
+---@type vim.lsp.Config
+return {
+  cmd = { 'rnix-lsp' },
+  filetypes = { 'nix' },
+  root_dir = function(bufnr, on_dir)
+    on_dir(vim.fs.root(bufnr, '.git') or vim.uv.os_homedir())
+  end,
+  settings = {},
+  init_options = {},
+}