feat(signaling server): add ready and sharing states mechanism

Added:
- Ready mechanism. To tell the caller that callee is already on the room view and ready to start sharing states (room id and caller)
- Sharing states mechanism. To tell each other the room id states and caller username. This shared states will be use by both the caller and callee views

Breaking changes:
- The calling is broken now

Notes:
- We are still using the '' room here