Logs: Add parameter for minimum severity

[m-mohr]

It could be useful to filter logs returned to a client by a minimum severity. So for example, if I pass severity=warning to the back-end, it should only return warnings and errors, but not info or debug messages.

[soxofaan]

Do you mean filtering when retrieving the logs? This would imply that the backend always has to keep track of all log levels, which might not be desirable for large jobs (debug level might be very verbose).

Alternative (or additional) approach: user has to specify minimum log level (e.g warning by default) when submitting the job

[m-mohr]

Yes, I was speaking about the retrieval. If the back-end doesn't provide some levels, that is fine. The contract doesn't enforce any level. Allowing the user to select what he wants to log when submitting the process is also a good idea.

[m-mohr]

The idea of a job/service/...-specific flag for log-levels came up again in an internal discussion where @clausmichele proposed:

Could we add the info about each partial result in the log if a debug flag has been activated? [...]