Add status field to API

[MorrisLaw]

We need a way to communicate to the user that the CR is misconfigured. Also, whether or not a Gateway exists in order to implement Policy Attachment correctly (see here).

Task:
The status of the targetRef referenced Gateway needs to be exposed to the controller responsible for applying policy. (One idea is to add a status field to Istio/api, but we should also consider existing solutions that may exist (e.g. kstatus)).

[linsun]

cc @therealmitchconnors who I recall tried to add this for Istio resources, also cc @howardjohn

[therealmitchconnors]

Istio resources already have a status field, which we mostly do not use. I like this idea, but it will require careful API design. For starters, I would consider using kstatus compatible conditions, unless there is a compelling reason to roll our own.

[MorrisLaw]

Thank you @linsun @therealmitchconnors. Is this where gateway status is updated?

[howardjohn]

Yes but only k8s Gateway. Istio status has been a bit different to date