Update plugins for Neovim integration docs (#8371)
This PR updates the editor integration section of the documentation for
Neovim.
* Removes the now archived `null-ls` plugin
* Add `nvim-lint` (for linters) and `conform.nvim` (for formatter)
plugins
Screenshot ref: https://github.com/astral-sh/ruff/assets/67177269/b7032228-57b1-4141-ae17-e186c4428b61
