[e.cash] add video background component

Summary: The site uses video backgrounds in several places. Adding a reusable component that can take the name of video file and render it

Test Plan: preview the site and see how it looks

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D13710