support monitoring NebulaGraph metrics and add help doc

[ZY945]

What's changed?

Checklist

• I hereby agree to the terms of the HertzBeat CLA
• I have read the Contributing Guide
• I have written the necessary doc or comment.
• I have added the necessary unit tests and all cases have passed.

Add or update API

• I have added the necessary e2e tests and all cases have passed.

[tomsun28]

👍👍LGTM！

[tomsun28]

hi please add the help and helplink like this:

# The description and help of this monitoring type
# 监控类型的帮助描述信息
help:
  zh-CN: Hertzbeat 将调用 HTTP API 接口，查看接口是否可用，并以 ms 为指标单位对其响应时间等指标进行监测。您可以先点击“新增 HTTP API”按钮并进行配置，或在“更多操作”中导入已有配置。
  en-US: The platform will invoke an HTTP API endpoint to verify its accessibility and monitor various metrics, including response time, measured in milliseconds (ms). <br>To set up this functionality, you could click the "Add HTTP API" button and proceed with the configuration or import an existing setup through the "More Actions" menu.
  zh-TW: Hertzbeat將調用HTTP API介面，查看介面是否可用，並以ms為名額組織對其回應時間等名額進行監測。 您可以先點擊“新增HTTP API”按鈕並進行配寘，或在“更多操作”中導入已有配寘。
helpLink:
  zh-CN: https://hertzbeat.com/zh-cn/docs/help/api
  en-US: https://hertzbeat.com/docs/help/api