Selective monitoring of Kubernetes workloads using annotations for (managed) agent fleet

Also known as hints based auto-discovery for agent enrolled in fleet
Picking up context from https://github.com/elastic/beats/issues/23876

We want to enable users to monitor Kubernetes workloads from the resource side for users of agent enrolled in fleet.

**User outcome**
Kubernetes users can declare their workloads and include hints, similar to those described in beats documentation [metricbeat](https://www.elastic.co/guide/en/beats/metricbeat/current/configuration-autodiscover-hints.html) and [filebeat](https://www.elastic.co/guide/en/beats/filebeat/current/configuration-autodiscover-hints.html) manifests and then expect agent whilst enrolled in fleet to pick these hints launch the proper config for it.

**Acceptance criteria**
On top of the outcome described above
- Users should have an accessible way to find the list of available hints
- Users should receive feedback for when a hint is not valid

** Child issues**
1. https://github.com/elastic/elastic-agent/issues/1350
2. https://github.com/elastic/elastic-agent/issues/1349
3. https://github.com/elastic/elastic-agent/issues/1347