Add truvvl embed

This merge request adds truvvl embeds as allowed embedded player.

There is an issue that the embed is stretched to full width, but since the format resembles a smartphone screen, the embed can only work if it has greater height than width.

On Peakd, an implementation as centered embed with the original dimensions height="700" width="375" and a max-height of "calc(100vh - 150px)" as style worked great. https://beta.peakd.com/hive-100037/@jpphoto/prague-to-sarajevo-cool-places-in-europe-europe-prague-zagreb-bosnia-20210420t103208397z

I haven't figured out how to implement this in Condenser. Any help will be greatly appreciated!