Update Creator Load check in Health-Check

[rgaudin]

In the health-check, we verify that the current worker load can be resolved within 2days.

The expected amount of time (it's not linear and can't be predicted) is based on a combination of magic values decided from empirical observations

See https://github.com/offspot/imager-service/blob/main/scheduler/src/routes/workers.py#L77

Those are based on pre-imager code that was a lot slower than current version. We should update it.
Given our build time is now solely based on download then upload speed, we could even decide on an average DL and UL speed and return a more realistic estimate based on this and the size.