feat: add setting for copilot enable or not.

[ayamir]

Not all users use copilot and not all situations we need it. So I add a switch to it. (Sorry for the wrong branch name)

[CharlesChiuGit]

Would also adding other AI engines toggle to core/settings.lua make sense? like tabline and codeium.
But the PR for now works as expected.

[CharlesChiuGit]

hmmm, it made a mess when i tried to include tabline and codeium. maybe just leave them along.

[fecet]

maybe also good to add some other AI stuff like chatgpt.nvim

[Jint-lzxy]

IMO we can leave this PR unchanged cause copilot has a large user base, thus shipping copilot with our base config makes sense to me. For those other plugins (possible candidates for extras), @fecet proposed in #888 (comment) that we can "use our custom loader (to) import extras like LazyVim". FWIW this is just trivial amount of work and can be implemented together w/ #931 😄

[ayamir]

Making it true by default won't influence the current user experience.

[ayamir]

maybe also good to add some other AI stuff like chatgpt.nvim

Haven't tried it because my free api key expired before lol