add lsp for nix

pkgs/nvchad/nvim/lua/configs/lspconfig.lua

@@ -12,3 +12,16 @@ for _, lsp in ipairs(servers) do
 		capabilities = capabilities,
 	})
 end
+
+lspconfig.nil_ls.setup({
+	on_attach = on_attach,
+	capabilities = capabilities,
+	cmd = { "nil" },
+	settings = {
+		["nil"] = {
+			flake = {
+				autoArchive = true,
+			},
+		},
+	},
+})