Move RESTful API and gRPC support into plugins.

[Jisu-Woniu]

The dependency tree is relatively large, so maybe we should consider moving some functionality into the plugin. This may help reduce compilation time and coupling.

依赖树相对较大，或许应该将一部分功能移至插件中。这样可能有助于减少编译时长，降低耦合度。

[Jisu-Woniu]

Prerequisite:

• Plugin API
  • Plugin configuration
    • Definition
    • Parsing
  • Judger abstraction
• Dependency injection (Maybe not needed since we can control them with feature flags now)
  Possible choices:
  • teloc
  • rudi