Tracking issue of painless integrating with Grafana via Prometheus plugin

[waynexia]

What type of enhancement is this?

User experience

What does the enhancement do?

Follows #1016, where some necessary APIs are implemented.

This issue is to track unexpected behavior or unimplemented features when connecting GreptimeDB with Grafana via its official Prometheus plugin.

• Error when saving GreptimeDB as Prometheus data source #3496
• Only have the numbers table on "metric" drop menu #3497

[tisonkun]

Once we're sure about the issue, perhaps open a subtask issue and link here. See https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/about-task-lists and pingcap/tidb#26022.

[yuanbohan]

I have tested Prometheus datasource in Grafana 10.0, and the following is the metadata Grafana needs:

Path	Form values	Query strings
POST /api/v1/query	query=1+1, time=4	empty
GET /api/v1/label/__name__/values?start=1710289581&end=1710311181	empty	start=1710289581,end=1710311181
POST /api/v1/labels	start=1710289583,end=1710311183,	empty
GET /api/v1/metadata	empty	empty
POST /api/v1/series	start=1710289589,end=1710311189,match=["{__name__="up"}"]	empty