feat(container_events): Add functionality to broadcast events to collaborators

[9trocode]

This pull request enhances the notification system for agent connection and disconnection events by ensuring that all collaborators with access to a given agent are notified, not just the owner. It introduces new logic to identify collaborators and broadcast relevant events to them, and adds a database method to efficiently retrieve collaborator user IDs for a specific container or agent.

Event Broadcasting Improvements:

• Updated NotifyAgentConnected and NotifyAgentDisconnected methods in container_events.go to broadcast agent connection and disconnection events to all collaborators who have access to the agent, in addition to the owner.
• Added a new helper method broadcastToCollaborators in container_events.go to handle broadcasting events to all relevant collaborators based on agent/container ID.

Database Support for Collaboration:

• Added GetCollaboratorUserIDsForContainer method to PostgresStore in postgres.go, which queries the database to return all unique user IDs of active participants in collaborative sessions for a specific container or agent. This supports the new event broadcasting logic.