Remove finalizers

[stone-z]

To support sharding metrics across exporters, it would be nice to get rid of the finalizers added by each controller to their watched aqua resources. The finalizers were only needed because it isn't possible to delete a metric from the golang prometheus client without specifying all of the labels for that metric -- in other words, we had to reconstruct the entire metric (so vulnerability details, etc.) in order to delete it. Finalizers were added to give the exporters an opportunity to clear the metrics before the report is deleted.

I've since implemented the functionality needed in the prometheus client, but this change has not been released yet.

With sharded metrics, the shard owner is responsible for clearing the finalizer after it has cleared its metrics for a given report. However, even the finalizer does not handle all cases where we might miss metrics, for example, when a statefulset is updated as described by #48. So, I'm committing a minor sin by using an untagged version of the prometheus client in order to a. solve the issue with stale metrics and b. hopefully get us closer to caching fewer reports per instance.

Checklist

• Update changelog in CHANGELOG.md.
• Make sure values.yaml and values.schema.json are valid.
• (Giant Swarm) If creating a release, bump the version and appVersion in Chart.yaml.

[fhielpos]

Nice 🚀

[stone-z]

@giantswarm/team-atlas as our resident metric gurus, if one of you has a quick moment today/tomorrow to see if any of this is completely backwards I'd appreciate it. I'll merge this tomorrow