Observability documents add the deployment manual for installing Grafana and Prometheus

## Describe the proposal
EN: Observability documents add the deployment manual for installing Grafana and Prometheus，The purpose of the manual is mainly to provide a quick start guide for those who use Dubbo observability. It does not need a complicated introduction to the principle, but only allows users to complete the software deployment and use in the production environment through documents.

中文：可观测性文档增加安装Grafana、Prometheus部署手册
为可观测性文档增加Grafana，Prometheus监控软件在生产环境的安装部署手册，手册目的是主要用于为使用Dubbo可观测性的人员提供快速入门的指南，无需复杂的原理介绍，只需要让用户可以通过文档完成软件部署、生产环境使用即可，尽可能得提供多种环境，如Linux 物理机、容器环境、K8S等环境的安装部署手册。

branch： refactor/next
Our observability doc file path is : content/zh-cn/overview/core-features/observability.md
Grafana install doc file path is:content/zh-cn/overview/core-features/install/grafana-install.md
Prometheus install doc file path is :content/zh-cn/overview/core-features/install/prometheus-install.md

Start with content/zh-cn/overview/core-features/observability.md and the existing Grafana and Prometheus files under content/zh-cn/overview/core-features/install/. Define the deployment coverage needed for production users across Linux physical machines, containers, and Kubernetes. Done means the observability documentation provides quick-start installation and usage guidance for those environments without requiring a separate principles introduction.

Written by the indexing model from the issue text.