Allow configuring tracing address as status.hostIP using the downward API

[fawadkhaliq]

Is your request related to a problem?
Some of the tracing providers support running agents as daemonsets (e.g. DataDog). If the agent is running on node locally and bound to the node local IP address, the tracing agent IP address will be different for every Envoy. AppMesh controller takes a global endpoint that is supposed to be same for every Envoy (either a service endpoint or a localhost for sidecar tracing agents). This works well for agents running at cluster level or as sidecars. However, anything running as a daemonset will not be able to receive traces.

Describe the solution you'd like
For tracing agents running as daemonsets, appmesh controller should provide a way to configure the host IP using fieldRef, which can be rendered using the Downward API. The downward API supports status.hostIP

Describe alternatives you've considered
Have the tracing agent support the k8s service topology to expose node local endpoints. This change is not on the controller side but on how the tracing agents are deployed so there's not much App Mesh controller can control

[fawadkhaliq]

Fixed here: #426