feat(orchestration-service): add getUserIntegrationsByUserUidAndCredentialType endpoint

Summary

This MR adds a new endpoint to retrieve user integrations with an optional filter to exclude already connected ones.

Changes

• New endpoint: getUserIntegrationsByUserUidAndCredentialType
• Added query parameter:
  • excludeConnected (optional)

Behavior

• When excludeConnected = true:
  • Returns only integrations not linked to any agent
• When not provided:
  • Returns all integrations

Benefits

• Enables frontend filtering of reusable integrations
• Improves flexibility in integration management