Revert 37882255d6ac5d15b7725df6a2c15a2c0c22928f (auto key generation)

We introduced a key generation mechanism that aimed to ease deployment.
In the end, it brought more complexity to the playbook and doesn't
scale.

Reverting the auto generation commit and instructing users to generate
their own keys.

Signed-off-by: Sébastien Han <sebastien.han@enovance.com>