Support LSPs in general

I would like to be able to use LSPs while using Joplin - for things such as linting, spell and grammar check, and now host-based (but would also work with cloud-based) AI assistants. I can use the external editor to leverage LSPs, but it would be much simpler if this could just be handled directly by Joplin - enabling a set of configurations to list LSPs to use, provide them args, etc.