Avoid logging that custom_tags or custom_metrics is not implemented on every request

[taavi-primer]

Currently the SeldonDeployments log on every request that custom_tags and custom_metrics are not implemented. This could be logged once on application start instead. Or at the very least moved to debug level.

2020-03-19 18:42:06,851 - seldon_core.user_model:client_custom_tags:131 - INFO:  custom_tags is not implemented
2020-03-19 18:43:10,423 - seldon_core.user_model:client_custom_metrics:304 - INFO:  custom_metrics is not implemented

[ChristophRose]

Even though this is closed, just a small note. To suppress this currently, add the following two functions to the model class:

def tags(self):
    return {}

def metrics(self):
    return []

[ukclivecox]

Thanks @ChristophRose If you think a small update to docs would help feel free to add a small PR.

[RafalSkolasinski]

I think such a note should specify for which wrapper version this is still relevant - latest s2i wrapper should properly have those logs at the debug level.