feat: add SetVehicleSpeed method to IMissionClientEx

A new method named SetVehicleSpeed was added to the IMissionClientEx interface. This method allows to change the speed of the vehicle while it's on a mission. This functionality was necessary to give users more control over the pace of the vehicle during mission execution.

Asana: https://app.asana.com/0/1203851531040615/1205990900963019/f

src/Asv.Mavlink/Microservices/Missions/Client/Ex/IMissionClientEx.cs

@@ -41,6 +41,7 @@ public static MissionItem AddSplineMissionItem(this IMissionClientEx vehicle, Ge
         item.Param4.OnNext(0);
         return item;
     }
+
     public static MissionItem AddNavMissionItem(this IMissionClientEx vehicle, GeoPoint point)
     {
         var item = vehicle.Create();
@@ -56,6 +57,7 @@ public static MissionItem AddNavMissionItem(this IMissionClientEx vehicle, GeoPo
         item.Param4.OnNext(0);
         return item;
     }
+
     public static MissionItem AddRoiMissionItem(this IMissionClientEx vehicle, GeoPoint point)
     {
         var item = vehicle.Create();
@@ -71,4 +73,17 @@ public static MissionItem AddRoiMissionItem(this IMissionClientEx vehicle, GeoPo
         item.Param4.OnNext(0);
         return item;
     }
+
+    public static MissionItem SetVehicleSpeed(this IMissionClientEx vehicle, float speed)
+    {
+        var item = vehicle.Create();
+        item.Command.OnNext(MavCmd.MavCmdDoChangeSpeed);
+        item.Current.OnNext(false);
+        item.Frame.OnNext(MavFrame.MavFrameGlobalInt);
+        item.MissionType.OnNext(MavMissionType.MavMissionTypeMission);
+        item.Param1.OnNext(1);
+        item.Param2.OnNext(speed);
+        item.Param3.OnNext(-1);
+        return item;
+    }
 }