Allow different language for each part of Copilot

[SilverBut]

Dup with #4158 but since it's closed I think a new issue can bring more background info.

I think it can be helpful to support different locales for different parts. For example, specify certain language (like Chinese) for commit messages only, while use default locale for everywhere else like Chat and terminal. This is necessary to align with history repository commits, while make other developers can use agent with their own language. Currently github.copilot.chat.localeOverride would affect everywhere including commit message generation, chat, edit, and terminal.