Integrate with Prometheus

[seeflood]

What would you like to be added:
Add a quickstart demo to show how Layotto is integrated with Prometheus.
Layotto already have the feature to export metrics data via http, see https://mosn.io/layotto/#/zh/start/trace/trace?id=metrics%e7%ae%a1%e7%90%86

Why is this needed:
Show users how to do integration

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity in the last 30 days. It will be closed in the next 7 days unless it is tagged (pinned, good first issue or help wanted) or other activity occurs. Thank you for your contributions.

[github-actions]

This issue has been automatically closed because it has not had activity in the last 37 days. If this issue is still valid, please ping a maintainer and ask them to label it as pinned, good first issue or help wanted. Thank you for your contributions.