Fix typo in CallerState enum

Author: namtzigla

tcnapi/exile/gate/v2/entities.proto

@@ -302,7 +302,7 @@ message CallerEvent {
 }
 
 enum CallerState {
-  CALLER_STATE_UNAVALIABLE = 0;
+  CALLER_STATE_UNAVAILABLE = 0;
   CALLER_STATE_IDLE = 1;
   CALLER_STATE_READY = 2;
   CALLER_STATE_HUNGUP = 3;