Add garbage collector trait

[astefanutti]

Fixes #211

The current algorithm relies on the discovery API to retrieve all the resources group and kind. That results in a collection that can be a bit slow (a couple of seconds). We may refine that step by white-listing or enlisting types to speed-up the collection duration.

[lburgazzoli]

I think there may be an issue here because the rest trait creates a config map when the integration is in its initialization phase and the gc runs in deploy phase:

• https://github.com/apache/camel-k/blob/master/pkg/trait/rest.go#L60
• https://github.com/apache/camel-k/blob/master/pkg/trait/rest.go#L143

[astefanutti]

Let me get back to work 😄!

[lburgazzoli]

We may introduce a concept of integration revision which gets incremented when the integration is in initialization phase and add labels/annotation to track to which revision resources are linked

[astefanutti]

Agreed. That was plan B, which is now A 😄!

Good news is that we have the integration revision for free thanks to f7714fe, as the activation of the status subresource triggers the metadata.generation field to increment in Kubernetes 1.11+.

[astefanutti]

Updated with the revision (metadata.generation) strategy.