Support serviceAnnotations to helm-metrics service

[carloscastrojumo]

This commit introduces a new Helm parameter, hubble.metrics.serviceAnnotations to enable annotations in helm-metrics service.

Example

Enable Kubernetes Integrations Autodiscovery used by Datadog:

hubble:
  metrics:
    serviceAnnotations:
      ad.datadoghq.com/endpoints.check_names: '["openmetrics"]'
      ad.datadoghq.com/endpoints.init_configs: '[{}]'
      ad.datadoghq.com/endpoints.instances: '[{"prometheus_url": "http://%%host%%:9091/metrics",
"namespace":"cilium-system","metrics": ["hubble*"]}]'

[kaworu]

No need for a full CI run, marking as ready-to-merge as reviews are done.

Thanks @carloscastrojumo for the patch!