Dynamic management of providers priority

[alambare]

Current implementation sort providers by a priority defined in configuration.

This leaves few limits:

• we always hit the quotas of the same provider first
• in case of a provider malfunction, the quality of service is impacted and the system does not react automatically

We could develop a provider priority orchestrator whose job would be to adapt the priority depending of the server behavior.
For example:

1. A provider stops responding. After a number of failed requests its priority is lowered (the provider could even be set unavailable)
2. A provider quotas got hit and the bandwidth is reduced. Below a certain target, the priority of the provider is lowered
3. Automatic rebalancing of provider priorities after multiple requests to spread the load

The providers should be checked after some time to reassess their situation.

The algorithm is left to be designed in this issue