Move lsp config to local file structure

.config/nvim/lsp/r_language_server.lua

@@ -0,0 +1,20 @@
+---@brief
+---
+--- [languageserver](https://github.com/REditorSupport/languageserver) is an
+--- implementation of the Microsoft's Language Server Protocol for the R
+--- language.
+---
+--- It is released on CRAN and can be easily installed by
+---
+--- ```r
+--- install.packages("languageserver")
+--- ```
+
+---@type vim.lsp.Config
+return {
+  cmd = { 'R', '--no-echo', '-e', 'languageserver::run()' },
+  filetypes = { 'r', 'rmd', 'quarto' },
+  root_dir = function(bufnr, on_dir)
+    on_dir(vim.fs.root(bufnr, '.git') or vim.uv.os_homedir())
+  end,
+}