🚸(frontend) highlight raised hands in participant's tile

Users's feedbacks. Raised hands in participants' tiles were not
highlighted enough.

It was discussed adding a colorful border around the participant's
tile (idea inspired by Jitsi). Nonetheless, it conflicts with the
current blue border, indicating when a participant is speaking.

Until this blue border is present, it's not a great idea having a
second border indicating a new level of informations.

@sampacoud requested a yellow-ish/colorful indicator of when a
participant raised her hand, inspired by Jitsi. However, I think
yellow color should be reserved for warning or dangerous action.

I chose to use a white background around the participant's name,
to reinforce the visual indication a participant has her hand
raised, while still being discreet. It's inspired by Gmeet.

src/frontend/src/features/rooms/livekit/components/ParticipantTile.tsx

@@ -123,13 +123,16 @@ export const ParticipantTile: (
                   className="lk-participant-metadata-item"
                   style={{
                     minHeight: '24px',
+                    backgroundColor: isHandRaised ? 'white' : undefined,
+                    color: isHandRaised ? 'black' : undefined,
+                    transition: 'background 200ms ease, color 400ms ease',
                   }}
                 >
                   {trackReference.source === Track.Source.Camera ? (
                     <>
                       {isHandRaised && (
                         <RiHand
-                          color="white"
+                          color="black"
                           size={16}
                           style={{
                             marginInlineEnd: '.25rem', // fixme - match TrackMutedIndicator styling