Evolve and Topic

In the context of heptapod#221 (closed), we'll need the topic extension to be active on the runner. For clarity, and since they are packaged together, I'll prefer to activate evolve as well. We should:

• add to our install instructions that topic and evolve should be installed and activated
• install hg-evolve in the helper Docker image. In Alpine, pip can be installed as pip install py-pip and that doesn't pull the whole jungle of C build toolchains
• activate evolve and topic in the helper Docker image. Via /etc/mercurial/hgrc.d should be fine.
• add options to the runner's pull in order to avoid some unnecessary and heavy operations such as obsmarker exchange