drivers: video: sensors: add a `sensor_skeleton.c` to speed-up contribution of simple sensors

[josuah]

Is your enhancement proposal related to a problem? Please describe.
There are more sensor contributions coming to Zephyr, from various location, and not yet guidelines for how to contribute them

Describe the solution you'd like
Having a sensor_skeleton.c would help maintainer communicate how they plan to integrate sensors, and help image sensor driver contributors to get going more quickly by skipping all the boilerplate.

Describe alternatives you've considered

• Have a video-wide skeleton instead
• Let things like they are now: no big priority.

Additional context
Other similar "template/skeleton/dummy" drivers:
https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/usb/udc/udc_skeleton.c
https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/display/display_dummy.c

[josuah]

Here is now a list snippets that can be interesting to add:

• https://github.com/zephyrproject-rtos/zephyr/pull/72254/files#r1605700254
• https://github.com/zephyrproject-rtos/zephyr/pull/72826/files/cfb16b7aa69948fea866f50fb42a226fa71aae10#diff-1fe02c52aeadf74decf28b87839e35abfd3f96e3548f5d1518276ca2439bd6af