feat(boards): add support for nrf52840dongle_nrf52840 (#3011)

This adds additional required configs for the Nordic NRF52840 Dongle (PCA10059),
which was already supported by Zephyr, but didn't have flash settings
and Bluetooth enabled.

Author: dapetcu21

app/boards/nrf52840dongle_nrf52840.conf

@@ -0,0 +1,12 @@
+# Copyright (c) 2025 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+CONFIG_ZMK_BLE=y
+CONFIG_ZMK_USB=y
+
+CONFIG_MPU_ALLOW_FLASH_WRITE=y
+CONFIG_NVS=y
+CONFIG_SETTINGS_NVS=y
+CONFIG_FLASH=y
+CONFIG_FLASH_PAGE_LAYOUT=y
+CONFIG_FLASH_MAP=y