use CAUS as auto scaler

[delvh]

Description TBA
(only possible once CAUS is done)

[delvh]

Still on hold as the original CAUS uses deprecated/ removed APIs,
and the new CAUS(es) are only a proof of concept.

[davidkopp]

A good alternative to CAUS could be KEDA.

I don't know much about CAUS, but at least the feature of autoscaling based on the rate messages arrive in a queue is also supported by KEDA (see e.g. mode MessageRate in the scaler RabbitMQ Queue).