Add configurable working directory/scope for context

[akamil-etsy]

Add an option to configure working directory/scope, if i work on a large repo i only need a particular subdirectory not the whole giant repo for context, right now this seems unusable as it attempts to send the whole repo to LLM (and thankfully fails). If it's hidden somewhere in the docs pls make it more prominent so first action user does when opening Roo Code and in Getting Started is configure working directory