modules: memfault: Default FW version is APPVERSION

Set default `CONFIG_MEMFAULT_NCS_FW_VERSION` to be pulled from a
`VERSION` file, if present, otherwise no default (which will cause a
build error).

This applies when `CONFIG_MEMFAULT_NCS_FW_VERSION_STATIC=y`.

With this change, all the needed version Kconfigs can be set from the
`VERSION` file, instead of needing to set them individually:

- `CONFIG_BT_DIS_FW_REV_STR`: used for BT DFU
- `CONFIG_MCUBOOT_IMGTOOL_SIGN_VERSION`: not strictly used, but nice for
  consistency
- `CONFIG_MEMFAULT_NCS_FW_VERSION`: used when reporting data to Memfault

Signed-off-by: Noah Pendleton <noah.pendleton@nordicsemi.no>

Author: noahp

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -878,6 +878,8 @@ Memfault integration
 
   * The ``CONFIG_MEMFAULT_DEVICE_INFO_CUSTOM`` Kconfig option has been renamed to :kconfig:option:`CONFIG_MEMFAULT_NCS_DEVICE_INFO_CUSTOM`.
   * The ``CONFIG_MEMFAULT_DEVICE_INFO_BUILTIN`` Kconfig option has been renamed to :kconfig:option:`CONFIG_MEMFAULT_NCS_DEVICE_INFO_BUILTIN`.
+  * The :kconfig:option:`CONFIG_MEMFAULT_NCS_FW_VERSION` Kconfig option will now have a default value set from a :file:`VERSION` file, if present in the application root directory.
+    Previously, this option had no default value.
 
 * Added a metric tracking the unused stack space of the Bluetooth Long workqueue thread, when the :kconfig:option:`CONFIG_MEMFAULT_NCS_BT_METRICS` Kconfig option is enabled.
   The new metric is named ``ncs_bt_lw_wq_unused_stack``.

modules/memfault-firmware-sdk/Kconfig

@@ -118,6 +118,7 @@ config MEMFAULT_NCS_FW_VERSION_PREFIX
 config MEMFAULT_NCS_FW_VERSION
 	string "Static firmware version to use"
 	depends on MEMFAULT_NCS_FW_VERSION_STATIC
+	default "$(APP_VERSION_TWEAK_STRING)" if "$(VERSION_MAJOR)" != ""
 	help
 	 When using a statically configured firmware version, this value
 	 will be reported to Memfault