Heptapod PAAS Runner: service aliases for Dependency Proxy

Changing the image name also changes the resulting default alias to something
like `foss.heptapod.net__heptapod__dependency_proxy__containers__redis`.
Of course this breaks the expectations of existing job definitions,
so we need to add an explicit alias in this case.

People using the Dependency Proxy have explictely put its prefix in their
URLs, so are either using the long impicit alias or simply defined their
own. That's why its not a problem with normal usage.

branch : heptapod
1 job for topic/heptapod/dependency-proxy-docker in 1 minute and 51 seconds
Status Name Job ID Coverage
passed test-python #249458