feat(nvim): Markdown handling improvements

- marksman: Trimmed config file: removed comments, remove default
  settings
- fix: ftplugin for codelens: provide current buffer
- new: Add obsidian.nvim plugin to replace markdown-oxide lsp

common/.config/nvim/lsp/markdown_oxide.lua

@@ -1,14 +0,0 @@
-return {
-    cmd = { "markdown-oxide" },
-    filetypes = { "markdown" },
-    root_dir = function()
-        return vim.fn.getcwd()
-    end,
-    settings = {
-        workspace = {
-            didChangeWatchedFiles = {
-                dynamicRegistration = true,
-            },
-        },
-    },
-}