Even if the engine could live with 2.7.0, the latest libpEpTransport needs 2.7.1.
Let us use it. Also add libpEpTransport as a dependency, even if the automatic
gitlab build system does not support it yet.
Adds simple jobs for building the the Engine for Debian 10.
Pre-built docker images containing Sequoia will be pulled down and used
to build the Engine. Currently the Sequoia version is just the latest
from the `pep-engine` branch. We should make this selectable in the near
future.
Upon successful compilation an image containing the build output will be
pushed to an internal docker registry.