Move lsp config to local file structure

.config/nvim/lsp/lean3ls.lua

@@ -0,0 +1,40 @@
+---@brief
+---
+--- https://github.com/leanprover/lean-client-js/tree/master/lean-language-server
+---
+--- Lean installation instructions can be found
+--- [here](https://leanprover-community.github.io/get_started.html#regular-install).
+---
+--- Once Lean is installed, you can install the Lean 3 language server by running
+--- ```sh
+--- npm install -g lean-language-server
+--- ```
+---
+--- Note: that if you're using [lean.nvim](https://github.com/Julian/lean.nvim),
+--- that plugin fully handles the setup of the Lean language server,
+--- and you shouldn't set up `lean3ls` both with it and `lspconfig`.
+
+---@type vim.lsp.Config
+return {
+  cmd = { 'lean-language-server', '--stdio', '--', '-M', '4096', '-T', '100000' },
+  filetypes = { 'lean3' },
+  offset_encoding = 'utf-32',
+  root_dir = function(bufnr, on_dir)
+    local fname = vim.api.nvim_buf_get_name(bufnr)
+    fname = vim.fs.normalize(fname)
+    -- check if inside elan stdlib
+    local stdlib_dir
+    do
+      local _, endpos = fname:find '/lean/library'
+      if endpos then
+        stdlib_dir = fname:sub(1, endpos)
+      end
+    end
+
+    on_dir(
+      vim.fs.root(fname, { 'leanpkg.toml', 'leanpkg.path' })
+        or stdlib_dir
+        or vim.fs.dirname(vim.fs.find('.git', { path = fname, upward = true })[1])
+    )
+  end,
+}