Add duration to review video thumbnails

[pwarren]

Describe what you are trying to accomplish and why in non technical terms
I want to be able to see a review clip's duration so that I can quickly see if the event is ~15s and hence probably a passing car, or more like 55 seconds to 2 minutes and is probably the postie

Describe the solution you'd like
Duration added to the overlay of the thumbnail on the 'review' page for events. Similar to the '[number] [seconds|minutes|hours] ago' and start date/time texts are added. 'mm:ss' would suffice, but there's probably already a time formatter that could be used.

Describe alternatives you've considered
Moving back to the 0.13 UI, I don't gel well with the new UI

Additional context
Discussed in #15905