Move lsp config to local file structure

.config/nvim/lsp/mm0_ls.lua

@@ -0,0 +1,15 @@
+---@brief
+---
+--- https://github.com/digama0/mm0
+---
+--- Language Server for the metamath-zero theorem prover.
+---
+--- Requires [mm0-rs](https://github.com/digama0/mm0/tree/master/mm0-rs) to be installed
+--- and available on the `PATH`.
+
+---@type vim.lsp.Config
+return {
+  cmd = { 'mm0-rs', 'server' },
+  root_markers = { '.git' },
+  filetypes = { 'metamath-zero' },
+}