Clean up fritz Docker builds w.r.t. configuration

[stefanv]

1. baselayer/config.yaml.defaults -> skyportal/config.yaml.defaults -> fritz.yaml (we can assume fritz is an end product, does not need customizable defaults)
2. Document that sections of config can be removed by specifying empty keys
3. Store only secrets and differential configs in deployment script, rest lives in fritz; this should also reduce chances of messing up the webpack build / template filling in the SOPS config
4. Remove route matching verification; quite possibly, user does not want that

[guynir42]

I think that given the trouble we've seen in recent deployments, this is worth pushing on...