non-API compliant UDP vs pre-defined process precedence

[jdries]

See first commit in this issue, due to a major performance and robustness problem in operations, I now gave predefined processes precedence over udp's. This avoids expensive udp lookups.

We need to further improve upon this quick solution.

Either we respect the API, and implement some caching of UDP names in the registry. This would not be super difficult, and allows us to respect the API.

The other solution is to double check if a user saves a udp, if the name is perhaps not a predefined process name, and throw an error instead of storing the UDP. That would make our backend more strict than what the API prescribes, but avoids ugly situations. I prefer this solution.

[soxofaan]

for additional context: also see eu-cdse/openeo-cdse-infra#325