feat(sisyfos): Send fadeTime with faderLevel if specified

[PeterC89]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Feature (sisyfos)

• What is the current behavior? (You can also link to an open issue here)
  Sisyfos cannot change fade time if the fader isPgm value isn't changed, so level changes cannot have adjustable fade time.

• What is the new behavior (if this is a feature change)?
  In conjunction with Allow fade times to be set with each level change tv2/sisyfos-audio-controller#271 the fadeTime property is sent with level changes.

• Other information:
  Tested against an unmodified version of Sisyfos (4.18.0) and appears to have no ill effects so should be fine to be in TSR until the Sisyfos PR is merged.

[jstarpl]

@PeterC89 Technically, the release50 is feature-frozen. How big of a problem would it be for you if we pushed this into release51 instead?

[PeterC89]

@jstarpl Not a problem at all, I can always build playout gateway manually if I need it urgently