Ghost text for code suggestions

[JamesHWade]

Should we add a ghost text option for code suggestions.

We would need to add:

• addin to trigger code suggestions
• package options to specify model
• ghost test functions + helpers

I implemented this in gpttools here.

I'm learning so much from this mistral implementation, and I'm curious at how you'd approach it differently.

[romainfrancois]

I like this, but I'm tentatively targetting the summer milestone so that the first version, aka the spring version will stay minimal.