feat(completion): add cmp-under-comparator

[Kamilcuk]

📑 Description

Add cmp-under-comparator to completion.

I tried to make the position of the comparator in nvim-cmp what users would "expect", and follow recommendation like from here. I think after "recentlyused" is the best position, first the ones you used, then the ones not string with dash ``.

ℹ Additional Information

[github-actions[bot]]

Review Checklist

Does this PR follow the [Contribution Guidelines](development guidelines)? Following is a partial checklist:

Proper conventional commit scoping:

• If you are adding a new plugin, the scope would be the name of the category it is being added into. ex. feat(utility): added noice.nvim plugin

• If you are modifying a pre-existing plugin or pack, the scope would be the name of the plugin folder. ex. fix(noice-nvim): fix LSP handler error

• [x] Pull request title has the appropriate conventional commit type and scope where the scope is the name of the pre-existing directory in the project as described above

• [x] README is properly formatted and uses fenced in links with <url> unless they are inside a [title](url)

• [x] Proper usage of opts table rather than setting things up with the config function.