AP_HAL_SITL: add camera simulation object

Add a new SIM_Camera object to SITL, similar to existing Sprayer and
Gripper payload simulations.

The camera simulation can be enabled via SIM_CAM_ENABLE and supports
triggering image capture via:
 - servo output (TRIG_SRV + TRIG_PWM)
 - GPIO pin (GPIO)

When triggered, the camera increments an internal image counter and
sends a GCS message indicating capture.

Author: TharakaUJ

libraries/AP_HAL_SITL/SITL_State.cpp

@@ -54,6 +54,11 @@ void SITL_State::_sitl_setup()
 #endif
 
         sitl_model->set_buzzer(&_sitl->buzzer_sim);
+#if AP_SIM_CAM_ENABLED && AP_SIM_MAX_CAMERAS > 0
+        for (uint8_t i = 0; i < AP_SIM_MAX_CAMERAS; i++) {
+            sitl_model->add_camera(&_sitl->camera_sim[i]);
+        }
+#endif
         sitl_model->set_sprayer(&_sitl->sprayer_sim);
         sitl_model->set_gripper_servo(&_sitl->gripper_sim);
         sitl_model->set_gripper_epm(&_sitl->gripper_epm_sim);