Make it easier to update forked agents

[ErikBjare]

The current way of forking the repo doesn't lend itself very well to updates to the template.

I wrote https://github.com/ErikBjare/gptme-agent-template/blob/master/scripts/compare.sh to help automate syncing an existing agent with the template (or vice versa), but feels like there should be a better way.

One option would be to make the whole harness a Python-package in itself, such that it becomes a Python dependency which can be updated. But not sure if that really makes sense here.