MiniVideoRecorder: Create Actions for starting/stopping video recording, and capturing the current video frame

We should support controlling video recording and image capture from the joystick.

Builds upon #609. Creating Actions from the widget itself makes it possible for the actions to be listed per widget instance, in a similar way to how the `VeryGenericIndicator` splits out different messages of the same type by their differentiator/ID field.

Base idea suggested by BillyBud in [this forum comment](https://discuss.bluerobotics.com/t/blueos-1-1-0-release/14931/11).

Start with the MiniVideoRecorder widget and issue #609, then trace how widget-defined Actions are registered and exposed to joystick controls. Done means the widget provides actions for starting and stopping recording and capturing the current frame, following the existing per-instance action pattern described in the issue.

Written by the indexing model from the issue text.