[Feature request] Add feature to do video recording even with screen off / locked

[bdutta]

Describe the solution you'd like
Normally the stock and other camera application require that the screen is ON all the time while the app is being used. It'd be good to have this app run a background service to continue with video recording say after the exposure and focus have been locked for a given camera sensor, thereby permitting usage of the app on old devices as a dash-cam or motovlogging action cam. Having the screen ON would needlessly consume extra battery. The hope is that when recording is started in this fashion, the app can record for unlimited time, i.e. up to the capacity of storage available minus some configurable buffer.

Additional context
(Add any other context or screenshots about the feature request here)