fix(video): restore the ability to set a minimum fps target (#4114)

src/config.h

@@ -141,6 +141,7 @@ namespace config {
     } dd;
 
     int max_bitrate;  // Maximum bitrate, sets ceiling in kbps for bitrate requested from client
+    double minimum_fps_target;  ///< Lowest framerate that will be used when streaming. Range 0-1000, 0 = half of client's requested framerate.
   };
 
   struct audio_t {