Add a second agent to the mocked-up agent repository

Our current mock of the MOSAICO repository (while WP2 is developing it) only returns the metamodelling-oriented collaboration agent we developed during T1.1. To help test the reference agent, we should add a second (more generalist) software engineering agent to the mix.

One option is the mini-SWE-agent:

https://github.com/SWE-agent/mini-SWE-agent

In this repository, we should only touch up the reference-repository to refer to it. The actual wrapping of the mini-SWE-agent would probably be best done in a new repository of its own.