[TT-3693] exposing https service using ingress

[asoorm]

trafficstars

By default, we have hardcoded Tyk's Ingress controller to only route to http backends.

api.Spec.Proxy.TargetURL = fmt.Sprintf("http://%s.%s.svc.cluster.local:%d", p.Backend.ServiceName, namespacedName.Namespace, p.Backend.ServicePort.IntValue())

If Tyk is routing to a service mesh, such as OSM, or ISTIO - it may be necessary to have the ingress route to a https backend. example:

https://github.com/openservicemesh/osm/blob/main/docs/patterns/ingress.md#exposing-an-http-or-https-service-using-ingress

In order to support this flow, it would be ideal if we can dynamically load the root certificate of the service mesh into the gateway certificate manager, then use this upstream certificate in the API Definition.

This way, we do not have to skip TLS verification for the upstream mesh gateway.