Improved Completions and Copilot logic

[Carson-Shaar]

Improve completion filtering
Revisit how completions/copilot suggestions are accepted (tab/enter)
Look into improving context for copilot
Better error handling for copilot, check for node installed and handle state better on the front end with more visual feedback/button locking/etc.

[Carson-Shaar]

SQL cells included
GPT completions, alternative to copilot