feat(backend): dev framework and example API code

[ev1lQuark]

What is the purpose of the change

• Give backend basic dev code, impl "SearchApplications" HTTP API.
• Define unified response body.
• Define paging and sorting common request params.
• Impl global error handling middleware.

How to verify this change

• Run dubbo-cp in terminal or use your IDE to debug dubbo-cp.
• Request new HTTP API by "Apifox" tool.