feat: add customer session refresh functionality and improve session management

- Introduced RealtimeCustomerSessionRefreshPayload and RealtimeCustomerSessionRefreshEvent types for handling session refresh events.
- Updated ws_service to verify customer session and handle session refresh notifications.
- Enhanced API client to manage customer session tokens and expiration.
- Implemented customer session validation and storage in session storage.
- Added functions to exchange and ensure customer sessions.
- Updated IM real-time connection to include customer session tokens in WebSocket requests.
- Modified SDK and widget configurations to support external IDs and user tokens.

internal/pkg/dto/response/customer_session_response.go

@@ -0,0 +1,13 @@
+package response
+
+type CustomerSessionCustomerResponse struct {
+	ID   int64  `json:"id"`
+	Name string `json:"name"`
+}
+
+type CustomerSessionExchangeResponse struct {
+	CustomerSessionToken string                          `json:"customerSessionToken"`
+	ExpiresAt            string                          `json:"expiresAt"`
+	IdentityKey          string                          `json:"identityKey"`
+	Customer             CustomerSessionCustomerResponse `json:"customer"`
+}