osd-clock: Display 12 Hour time format

[caslicco]

I'm new to coding and to mpv. I want to make 2 modifications to the osd-clock script:

1. Display time in the 12 Hour format.
2. Toggle the clock ON at startup, and define a key to toggle the clock OFF

[Cananbolt]

I can help you with your first request.

Go to line 24 where it states format = "%H:%M",

Change the H to I (uppercase i)