Allow configurable upstream timeout for envoy

[ukclivecox]

Presently hardwired to 60s. This could initial be changed to 0 to disable timeout. Ideally, a setting per Model/Pipeline.

[mafs12]

@cliveseldon how can I currently increase that timeout for all requests to all Models? Env var in the envoy pod? And which timeout are we talking about when model takes too long to respond?

[mafs12]

Found it: https://github.com/SeldonIO/seldon-core/blob/v2.7.0-rc1/scheduler/pkg/envoy/resources/resource.go#L58. Already set to 0.