Add the HTTP API for querying pipelines

[zyy17]

What type of enhancement is this?

User experience

What does the enhancement do?

Although we decide not to expose many HTTP APIs for DB, it will be natural to have an HTTP API for querying pipelines except for the create and delete operation for pipeline management.

For developer experience, when they create a pipeline, it will be convenient to use a similar API to query the pipeline unless using SQL to query greptime_private, for example:

curl -XGET "http://localhost:4000/v1/events/pipelines/test?db=public"

Implementation challenges

No response