Allow custom video player with video embed

[drewbaker]

I need to upgrade the video embed block to use the custom video player (and we consider the player closed source), but only if it's available as not all sites use the custom player.

I did this for these sites:
https://github.com/funkhaus/mirada-frontend/blob/master/components/gutenberg/Embed.vue
https://github.com/funkhaus/missing-pieces-frontend/blob/master/components/gutenberg/Embed.vue
https://github.com/funkhaus/superbloom-frontend/blob/master/components/gutenberg/Embed.vue

[drewbaker]

Closed with 08d9d48