🚀 Make image thumbnail also video thumbnail in video playlist widget

- [x] I have searched for similar features requests in both open and closed tickets and cannot find a duplicate.
- [x] The feature is still missing in the latest stable version of Elementor ( Elementor Pro. )

**What problem is your feature request going to solve? Please describe.**
Improves the look of the front end / makes it look more professional

**Describe the solution you'd like**
Make thumbnail image also video thumbnail image

**Describe alternatives you've considered**
Use alternative to video playlist widget instead.
Leave it blank.

**Additional context**
This is the 2nd big issue with this widget (the other is starting all videos muted). It's not far off being ill-advisable to use.