libcamera: parse arrays for options

[ayufan]

This does that by trying to parse value,
and then advancing pointer. It checks if the
string ends or is split by comma.

With collaboration from @arekm. Take a look at:

• 1) Fix splitting options by coma. 2) Also decode POST arguments. 3) Fix handling Array of Rectangles #170
• libcamera: parse arrays for options #172
• Parse control arrays #176