Only check for docs if the user wants to run the task.

[gperetin]

We want to fetch external docs only if the user wants to execute the task (not for skipped tasks).

This is not ideal implementation, as it's not intuitive in the Developer agent when we check for docs, but I think it's better than the alternative.

Initially, I wanted to move the external docs check into Developer agent, sort of like what get_relevant_files does, but gave up, as that would clobber the Developer quite a lot - external docs is much more complex, does 2 LLM requests and 2 API requests.

The complexity arises from the fact how control flow is done between agents, which is through AgentResponse, and a bunch of checks in Orchestrator and various agents. I'm open to suggestions on how to make this better.