enhance doc about configuring apicast to use opentracing

The following two sections need to be reviewed

Section 1.4 https://access.redhat.com/documentation/en-us/red_hat_3scale_api_management/2.12/html/administering_the_api_gateway/introduction-to-advanced-operation-of-threescale-apicast-api-gateway_api-gateway-apicast#configuring-apicast-to-use-opentracing

Section 1.5 Installing Jaeger on your OpenShift instance https://access.redhat.com/documentation/en-us/red_hat_3scale_api_management/2.12/html/administering_the_api_gateway/introduction-to-advanced-operation-of-threescale-apicast-api-gateway_api-gateway-apicast#installing-jaeger-on-your-openshift-instance

Both the 3scale operator opentracing setup support (https://github.com/3scale/3scale-operator/blob/master/doc/apimanager-reference.md#APIcastOpenTracingSpec) and apicast operator opentracing setup support (for self-managed apicast deployments) (https://github.com/3scale/apicast-operator/blob/master/doc/apicast-crd-reference.md#OpenTracingSpec). . That support should be used in the user guides to setup gateway tracing.

Also one wrong link: Upstream project for OpenTracing and Jaeger integration -> https://github.com/3scale/apicast. It should be https://github.com/jaegertracing/jaeger