Make Music fade out times configurable

[AlexVild]

Is your feature request related to a problem? Please describe.
It would be nice if there was an easy way (client config, likely) to adjust how quickly songs fade in and out of eachother. Going a step further, it might also be nice for the Fade Out BGM and Play Music events to provide those options to the user as well.

Sound control is very important for cinematic effect.

Describe the solution you'd like

• A client config option for fade in and fade out times
• Optionally, additional config on the Fade Out BGM and Play Music events that allow the user to set custom fade in/fade out times for each.

Additional context
One thing to note is that the code in the area is a bit hard to follow. Cheshire commented a section of Update() that may provide value, so I'll put it here:

var currentTime = Globals.System.GetTimeMs();
    // Do we have a valid fade timer?
    if (sFadeTimer != 0 && sFadeTimer < currentTime)
    {
        // Are we actually fading out a song?
        if (sFadingOut)
        {
            // Lower the volume by one for our current song.
            sMyMusic.SetVolume(sMyMusic.GetVolume() - 1, true);
            
            // Are we already at minimum volume?
            if (sMyMusic.GetVolume() <= 1)
            {
                // Yes, stop our current song and play our next!
                StopMusic();
                PlayMusic(sQueuedMusic, 0f, sQueuedFade, sQueuedLoop);
            }
            else
            {
                // No, set our fade timer to the current time PLUS our defined wait time
                // This way we don't lower the volume a little further for a while.
                sFadeTimer = currentTime + (long)(sFadeRate / 1000);
            }
        }
        else
        {
            // We're not fading out a song but fading it in!
            sMyMusic.SetVolume(sMyMusic.GetVolume() + 1, true);
            
            // Are we at max volume?
            if (sMyMusic.GetVolume() < 100)
            {
                // No, set our fade timer to the current time PLUS our defined wait time
                // This way we don't raise the volume a little further for a while.
                sFadeTimer = currentTime + (long)(sFadeRate / 1000);
            }
            else
            {
                // We're fully faded in, so invalidate the fade timer.
                sFadeTimer = 0;
            }
        }
    }