[amp-story-player] Load documents from the cache #27588
Description
Support loading the stories from the cache unless the publisher opts-out.
API will look as following:
<amp-story-player> // does not load from the cache (the default)
<amp-story-player amp-cache="cdn.ampproject.org"> // loads from cdn.ampproject.org (explicitly)
<amp-story-player amp-cache="cdn.example.com"> // loads from cdn.example.com (explicitly)
/cc @ampproject/wg-stories