Use sinkbinding in operator

[nicolaferraro]

Following apache/camel-k-runtime#372 we should enable the following two scenarios in the operator:

1) Auto-publish as source via sinkbinding

When writing an integration like:

from("xxx").to("knative:endpoint/xxx")

Instead of looking up directly xxx, we can create a sinkbinding on the subresource we create (deployment/cronjob/kservice), so that knative injects the correct references.

This allows an integration to be directly seen as Knative source directly.

The behavior should not be the default until sinkbinding gets more stable.

2) Allow users to do sinkbinding on Integrations

While it's not currently possible to select a Camel K resource for sinkbinding, the subresources can be selected via label for sinkbinding.

So a user should be able to define an integration with an empty sink, e.g.:

from("...").to("knative:endpoint")

(or something similar, to be documented)

And the binding to the actual sink should be provided by the user via a manually created sinkbinding.

If no sinkbinding is provided by the user, the integration should fail at runtime (but not being blocked by the operator).