Allow `assign-to-agent` safe output to select the repo that the PR should be created in

[steliosfran]

Our issues are located in a different repository than our codebases.

Assigning an issue to Copilot and selecting the target repository is available through the GitHub UI (see https://github.com/orgs/community/discussions/173575)

But that doesn't seem to be supported when assigning an issue to Copilot using the agentic workflow: https://github.github.com/gh-aw/reference/safe-outputs/#assign-to-agent-assign-to-agent

The assign-to-agent safe output has a target-repo param, but that seems to be the repo where the issue lives, not the repo where we want to open the pull request in.

Am I missing something or is this a missing feature that might be implemented in the future?