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

src/config.cpp

@@ -504,7 +504,8 @@ namespace config {
       {}  // wa
     },  // display_device
 
-    0  // max_bitrate
+    0,  // max_bitrate
+    0  // minimum_fps_target (0 = framerate)
   };
 
   audio_t audio {
@@ -1146,6 +1147,7 @@ namespace config {
     }
 
     int_f(vars, "max_bitrate", video.max_bitrate);
+    double_between_f(vars, "minimum_fps_target", video.minimum_fps_target, {0.0, 1000.0});
 
     path_f(vars, "pkey", nvhttp.pkey);
     path_f(vars, "cert", nvhttp.cert);