Fix error handling for invalid responses
At the moment network-dev is broken and returns HTTP instead of JSON when trying to schedule observations. This patch improves the error handling, but doesn't resolve the root issue with scheduling in satnogs-network.
Additional changes belong to:
- container setup
- image creation & caching
- a fix to the built-in SatNOGS API client to support empty list responses --> new stations with 0 previous observations are supported by the auto-scheduler now