Add more playback speed (0.75 and 1.25)

Those speeds are much more closer to the normal speed. They are useful for listening to human speeches.

client/src/assets/player/peertube-player.ts

@@ -49,7 +49,7 @@ function getVideojsOptions (options: {
     poster: options.poster,
     autoplay: false,
     inactivityTimeout: options.inactivityTimeout,
-    playbackRates: [ 0.5, 1, 1.5, 2 ],
+    playbackRates: [ 0.5, 0.75, 1, 1.25, 1.5, 2 ],
     plugins: {
       peertube: {
         autoplay: options.autoplay, // Use peertube plugin autoplay because we get the file by webtorrent