Preferences: Add option to control preloading of video data (#4122)

This PR adds a configuration option to control the preloading of video data on
page load with the HTML5 'preload'[1] attribute on the `<video>` element.

The option is enabled by default, meaning that the `preload` attribute's value
will be 'auto'. If users want to prevent preloading of video data, they
can disable the option, which will set the attribute value to 'none'.

[1](https://www.w3schools.com/tags/att_video_preload.asp)

Closes issue 4110

src/invidious/views/components/player.ecr

@@ -1,5 +1,6 @@
 <video style="outline:none;width:100%;background-color:#000" playsinline poster="<%= thumbnail %>"
     id="player" class="on-video_player video-js player-style-<%= params.player_style %>"
+    preload="<% if params.preload %>auto<% else %>none<% end %>"
     <% if params.autoplay %>autoplay<% end %>
     <% if params.video_loop %>loop<% end %>
     <% if params.controls %>controls<% end %>>