[Feature] Enable focusing on specific files for a review

[ryan-at-kettle]

Some PRs are larger than the limit of tokens. Enable directing the review to only the files the user is concerned about.

[wololodev]

a quick fix would be to review files that arent "viewed" (which is collapsed in PR mode)

but we can also use langchainjs to build short term memory and have multiple prompts (though that would require openai key instead of relying on chatgpt proxy)