[FEATURE] Markdown LSP

[pbek]

It (maybe) would be great to have integration for a Markdown LSP, like https://github.com/artempyanykh/marksman.

[pbek]

26.2.9

• Added experimental Markdown LSP support with settings for server command/arguments
  (for #3467)
  • The integration is experimental and currently provides completions via the autocomplete action
  • LSP info logs are no longer shown as warnings; only error-like stderr output is surfaced
  • Diagnostics published by the LSP server are now displayed as wave underlines in the editor;
    severity is reflected by color: red for errors, orange for warnings, blue for information,
    and green for hints
  • Hovering over a diagnostic underline shows a tooltip with the diagnostic message
  • Diagnostics are cleared automatically when switching to a different note