refs https://github.com/TryGhost/Team/issues/1229
- changed the video card image so it uses an aspect-ratio box set to the aspect ratio of the video, with the image using `object-fit: cover` to match the background image behavior in the front-end
refs https://github.com/TryGhost/Team/issues/1229
- using the images API lets us separate the auto-generated thumbnail and custom thumbnail
- added `customThumbnailSrc` to video card payload and switched settings panel uploader to store upload result there
- switched image display to fallback from custom thumbnail to auto-generated thumbnail
refs https://github.com/TryGhost/Team/issues/1229
- mostly mirrors image card functionality but rebuilt with more modern syntax
- when uploading a video the size and duration is extracted along with a screen capture of the video from 0.5s in, the screen capture is uploaded once the video finishes because we need to use the uploaded video url as a reference to attach it as a thumbnail via the API
- the captured screenshot is currently what's shown in the card
To be implemented:
- "incomplete" state when video has been uploaded but not a thumbnail
- uploader in settings panel to change the video thumbnail
- play button overlay _or_ switch to `<video>` so it can be previewed
