feat(agentflow): make client-specific knowledge fields for agent nodes (#6226)

- Updated Agent node to include 'client' property for 'agentKnowledgeDocumentStores' and 'agentKnowledgeVSEmbeddings', allowing differentiation between 'agentflowv2' and 'agentflowsdk'.
- Added tests to ensure correct filtering of knowledge fields based on client type.