Add ability to change stream resolution in GUI

[Abysmalduck]

Currently, Screego streams at the monitor's native resolution (e.g., Quad HD/1440p). On higher-resolution displays, this causes severe FPS drops (to near zero) due to excessive bandwidth/encoding demands.
Manually modifying the useRoom.ts file to enforce resolution constraints resolves the issue:

//useRoom.ts; share function
try {
 const constraints = {
 video: {
 frameRate: loadSettings().framerate,
 width: { ideal: 1600, max: 1600 },
 height: { ideal: 900, max: 900 }
 },
 audio: { 
 echoCancellation: false,
 autoGainControl: false,
 noiseSuppression: false,
 googAutoGainControl: false, }
 };

 stream.current = await navigator.mediaDevices.getDisplayMedia(constraints);

 const [videoTrack] = stream.current.getVideoTracks(); //second time for firefox
 await videoTrack.applyConstraints({
 width: { ideal: 1600, max: 1600 },
 height: { ideal: 900, max: 900 },
 frameRate: loadSettings().framerate
 });
 }

That code works well in Chrome and Firefox, so maybe it's good to add configurable resolution settings in the Screego GUI to let users customize resolution of stream.