Improve duration metrics

[seaneagan]

Issues

1. release_phase_duration_seconds should not reference "phase", and should instead reference "action" as per the "action" label it supports.
2. release_duration_seconds as a name implies an entire release process, i.e. multiple sync attempts when retries are necessary. However the data it exposes is only about a single sync attempt.
3. Documentation of the labels and actions is missing.
4. The largest finite bucket max is currently 5 minutes. Larger buckets e.g. 10 minutes and 30 minutes could be useful as well for long running releases e.g. those which may need for dependencies to become ready before completing, or those which timeout after e.g. 15 minutes.
5. The release_name self-documents that it refers to the releaseName and not the metadata.name of the HelmRelease, but the namespace label does not self-document that it refers to the targetNamespace and not metadata.namespace of the HelmRelease.

Proposal

Deprecate these metrics (still support for some time but remove from docs) and add and document a new metric called release_action_duration_seconds (corrected name) which also encompasses release_duration_seconds functionality by adding support for a sync value to the action label. Also this metric would replace the namespace label with a target_namespace label.