Develop openapi for ticdc.

[asddongmen]

Feature Request

This issue proposes the design plan of the TiCDC HTTP API, which aims to reconstruct the existing API of CDC and add new APIs to meet new requirements and facilitate future maintenance and expansion.

Describe the feature you'd like:

• API is simple, unified and easy to use.
  - [ ] Provide unit test and be able to conduct complete function test on API. [WIP] (should open another issue to do this job)
• Provide integration test for all APIs.
  - [ ] Transform the old cli to use the new API. [Delay] (should open another issue to do this job)
• Provide complete API usage documents.
• Automatically forward the request to the owner.

There are 16 APIs:

• create changefeed
• update changefeed
• get changefeed
• list changefeeds
• pasue changefeed
• resume changefeed
• delete changefeed
• move table
• rebalance table
• get processor
• list processors
• list captures
• get status of a server
• health check of cdc cluster
• get debug info of cdc
• change log level of cdc

[asddongmen]

done