feat(plugins): add the ability to disable todo-comments.nvim in zen-mode

[paulhdk]

I'm an avid and happy user of the todo-comments.nvim plugin, but when writing (text, not code) in zen mode, I personally find the highlights to be distracting sometimes. Since todo-comments.nvim is also part of the @folke ecosystem of plugins, I thought an option to explicitly disable the highlights made by the plugin would make a nice addition to the zen-mode.nvim.

[github-actions[bot]]

This PR is stale because it has been open 60 days with no activity.

[folke]

ty!