Apps watcher PoC

[luizbafilho]

Very rough implementation of HelmReleases watchers that would trigger pipeline updates.

It doesn't not implement the whole solutions described here: https://github.com/weaveworks/weave-gitops-enterprise/issues/1481

Missing parts are:

• The controller needs to label the AppRef with metadata so we can identify its pipeline when an update event comes in.
• We need to implement a watcher for GitopsClusters so we can update the list of informers
• We need to loop through all informers and start the watching, right now I hardcode to the management cluster.
• We need actually trigger the promotion, now it just logs.