dox: doxygen: add third_party group

Add a new top-level group for APIs that interact with third-party
services or applications. Included in the group:

- MCUboot image control API
- Hawkbit
- UpdateHub

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

doc/_doxygen/groups.dox

@@ -43,4 +43,9 @@
 @{
 @}
 
+@brief APIs to interact with third-party services or applications
+@defgroup third_party Third-party
+@{
+@}
+
 */

include/zephyr/dfu/mcuboot.h

@@ -26,6 +26,7 @@
  * @brief MCUboot public API for MCUboot control of image boot process
  *
  * @defgroup mcuboot_api MCUboot image control API
+ * @ingroup third_party
  * @{
  */
 

include/zephyr/mgmt/hawkbit.h

@@ -7,7 +7,7 @@
 /**
  * @brief hawkBit Firmware Over-the-Air for Zephyr Project.
  * @defgroup hawkbit hawkBit Firmware Over-the-Air
- * @ingroup lib
+ * @ingroup third_party
  * @{
  */
 #ifndef ZEPHYR_INCLUDE_MGMT_HAWKBIT_H_

include/zephyr/mgmt/updatehub.h

@@ -7,7 +7,7 @@
 /**
  * @brief UpdateHub Firmware Over-the-Air for Zephyr Project.
  * @defgroup updatehub UpdateHub Firmware Over-the-Air
- * @ingroup lib
+ * @ingroup third_party
  * @{
  */