[Features] KubeBlocks integration with users' existing monitoring stack

[nashtsai]

What is the user interaction of your feature
KubeBlocks integration with users' existing monitoring stack.

Is your feature request related to a problem? Please describe.
Take following 2 K8s platform examples:

1. EKS + AMP + AMG
2. Red Hat OpenShift Service on AWS (ROSA) with its own monitoring stack (Prometheus + AlertManager + Thanos)

That KubeBlock doesn't provide integration how-to for existing monitoring stack, it basically means that all the alert rules, dashboards, and notification are proprietary only.

Describe the solution you'd like
Integration pattern API models for existing monitoring stack, that allows me to have a unified monitoring management, I would suggest leverage existing Prometheus Operator and Grafana Operator APIs:

• PrometheusAgent prometheusagents.monitoring.coreos.com for handling remote write config
• AlertmanagerConfig alertmanagerconfigs.monitoring.coreos.com for handling to custom alert receiver
• GrafanaDashboard grafanadashboards.grafana.integreatly.org for Dashboard management

[nashtsai]

ref: #3674

[nashtsai]

@yimeisun @yangmeilly Datadog integration seems just work with our current Prometheus annotations':

https://docs.datadoghq.com/containers/kubernetes/prometheus/?tab=kubernetesadv2#basic-configuration

I would suggest provide Datadog addon, ref. following doc:

https://docs.datadoghq.com/containers/kubernetes/installation/?tab=helm#installation

[yimeisun]

We will introduce the monitoring operator and the corresponding API in the next version, which will support flexible deployment and scheduling of agents, as well as provide user extension capabilities.

[nayutah]

Supported in enterprise-edition.