feat: Add Citations and Attributions to Agent Node

[chiehw]

Fixes #17986

Related PR:

• [x] https://github.com/langgenius/dify-plugin-sdks/pull/107
• [x] https://github.com/langgenius/dify-plugin-daemon/pull/236
• [x] https://github.com/langgenius/dify-plugin-sdks/pull/123
• [x] https://github.com/langgenius/dify-official-plugins/pull/814
• [x] https://github.com/langgenius/dify-plugin-daemon/pull/253
• [ ] https://github.com/langgenius/dify-official-plugins/pull/895

Summary

1. Support var-selector type parameters(Prerequisites): This parameter supports the use of scope to configure the selectable variable type. The optional scope is:

class DefaultValueType(StrEnum):
  STRING = "string"
  NUMBER = "number"
  OBJECT = "object"
  ARRAY_NUMBER = "array[number]"
  ARRAY_STRING = "array[string]"
  ARRAY_OBJECT = "array[object]"
  ARRAY_FILES = "array[file]"

2. Support retriever_resources type messages: This feature allow agent strategy return Citations and Attributions.

Screenshots

Before	After

Checklist

[!IMPORTANT]
Please review the checklist below before submitting your pull request.

• [x] This change requires a documentation update, included: Dify Document
• [x] I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• [x] I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [x] I've updated the documentation accordingly.
• [x] I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[oneness0]

Please approve it. @crazywoola

[zhudongwork]

In the official environment, after upgrading the agent policy plugin to the latest version, I still cannot achieve the agent node reference display functionality.