Add logging functions

[twistedfall]

Adds the functions to control libcamera logging. Some notes on the implementation:

• logSetStream only allows selection from stdout and stderr due to complexity of handling C++ ostream
• libcamera_logging_target doesn't contain all enum values because the documentation mentions that only those 2 are valid to be passed to logSetTarget
• log_set_level() is implemented as the CameraManager instance method because in my testing I was only be able to see the effect of this function after the creation of CameraManager, any calls before that seem to be ignored.

[chemicstry]

Hey, thanks for the PR!

Looks good from a first glance.

Unfortunatelly, I'm currently traveling and won't have access to a linux machine to properly test/review this for a couple of weeks.

[twistedfall]

Sorry that it took me so long to review.

Seems to work okay, but could you add an example demonstrating how to use this?

Sure thing!

[twistedfall]

@chemicstry Can you please check if that's what you had in mind?

[chemicstry]

I think it looks good now, thanks!