Renaming Instance Gateway + APIs

[Rob Scott]

Hey Everyone,

I've written up a doc that proposes renaming our llm-instance-gateway subproject and the APIs it contains. In both cases, I'm hoping the updated names are more representative of the intended scope of the project and APIs.

Will appreciate any feedback on the doc. I'm going to rely on lazy consensus here, and will move forward with PRs on Tuesday unless we get feedback suggesting a different approach.

Thanks!

Rob