mgmt: mcumgr: grp: settings_mgmt: copy source form zephyr

Copy source code from sdk-zephyr codebase:
settings_mgmt.c

cherry-pick from sdk-zephyr 9dc45313c55a945b6fe42be2f848ac29580a60a3

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>

Author: nvlsianpu

scripts/ci/license_allow_list.yaml

@@ -54,6 +54,7 @@ Apache-2.0: |
   ^nrf-bm/subsys/mgmt/mcumgr/grp/os_mgmt/Kconfig
   ^nrf-bm/subsys/mgmt/mcumgr/grp/settings_mgmt/CMakeLists.txt
   ^nrf-bm/subsys/mgmt/mcumgr/grp/settings_mgmt/Kconfig
+  ^nrf-bm/subsys/mgmt/mcumgr/grp/settings_mgmt/src/settings_mgmt.c
   ^nrf-bm/subsys/mgmt/mcumgr/Kconfig
   ^nrf-bm/subsys/mgmt/mcumgr/mgmt/CMakeLists.txt
   ^nrf-bm/subsys/mgmt/mcumgr/mgmt/Kconfig

subsys/mgmt/mcumgr/grp/settings_mgmt/CMakeLists.txt

@@ -7,4 +7,4 @@
 # Settings management group public API is exposed by MCUmgr API
 # interface, when settings management is enabled.
 zephyr_library_named(mgmt_mcumgr_grp_settings)
-zephyr_library_sources(${ZEPHYR_BASE}/subsys/mgmt/mcumgr/grp/settings_mgmt/src/settings_mgmt.c)
+zephyr_library_sources(src/settings_mgmt.c)