[epic][plugin] Implement Stage Plugins

[t-kikuc]

What would you like to be added:

Support the following stages in the plugin architecture.

• WAIT Stage
  • Init server Init grpc server of wait stage plugin #5445
  • Use metadata store
  • Core logic of waiting (without handling the stopSignal)
  • Optimize stage config location
  • Optimize skipOn option location
• WAIT_APPROVAL Stage
• ANALYSIS Stage

Note: We've not determined how to support the SCRIPT_RUN Stage in the plugin architecture.

Why is this needed:

Stages will also become plugins, not built-in code.
That will extend the flexibility of pipelines.