feat: Support multiple knowledge base binding in pipelines (#1766)

* Initial plan

* Add multi-knowledge base support to pipelines

- Created database migration dbm010 to convert knowledge-base field from string to array
- Updated default pipeline config to use knowledge-bases array
- Updated pipeline metadata to use knowledge-base-multi-selector type
- Modified localagent.py to retrieve from multiple knowledge bases and concatenate results
- Added KNOWLEDGE_BASE_MULTI_SELECTOR type to frontend form entities
- Implemented multi-selector UI component with dialog for selecting multiple knowledge bases

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

* Add i18n translations for multi-knowledge base selector

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

* Fix prettier formatting errors in DynamicFormItemComponent

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

* Add accessibility attributes to knowledge base selector checkbox

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

* fix: minor fix

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>
Co-authored-by: Junyan Qin <rockchinq@gmail.com>

templates/default-pipeline-config.json

@@ -45,7 +45,7 @@
                     "content": "You are a helpful assistant."
                 }
             ],
-            "knowledge-base": ""
+            "knowledge-bases": []
         },
         "dify-service-api": {
             "base-url": "https://api.dify.ai/v1",