fix(elixir): add missing lspconfig

lua/lazyvim/plugins/extras/lang/elixir.lua

@@ -5,6 +5,14 @@ return {
       root = "mix.exs",
     })
   end,
+  {
+    "neovim/nvim-lspconfig",
+    opts = {
+      servers = {
+        elixirls = {},
+      },
+    },
+  },
   {
     "nvim-treesitter/nvim-treesitter",
     opts = { ensure_installed = { "elixir", "heex", "eex" } },