[nrfconnect] Refactored configuration for the nrfconnect examples

nrfconnect platform uses Kconfig overlays and defaults in a way
that is not consistent with the nRF Connect SDK recommendations

* Created Kconfig.defaults that set default configs common
for all examples (replaced sample-defaults.conf)
* Created Kconfig.features that allows to configure set
of options within single feature using single option
* Replaced approach of adding overlays in example cmake file
with the pattern of placing prj.conf files in a
configuration/build-target/ location that allows adding config
files to the build automatically by the toolchain.
* Created debug and release configuration variants for several
examples.

.github/workflows/examples-nrfconnect.yaml

@@ -175,7 +175,7 @@ jobs:
             - name: Build example nRF Connect SDK All Clusters App on nRF52840 DK
               timeout-minutes: 10
               run: |
-                  scripts/examples/nrfconnect_example.sh all-clusters-app nrf52840dk_nrf52840 -DBUILD_WITH_DFU=1
+                  scripts/examples/nrfconnect_example.sh all-clusters-app nrf52840dk_nrf52840 -DCONFIG_CHIP_OTA_REQUESTOR=y
                   .environment/pigweed-venv/bin/python3 scripts/tools/memory/gh_sizes.py \
                     nrfconnect nrf52840dk_nrf52840 all-clusters-app \
                     examples/all-clusters-app/nrfconnect/build/zephyr/zephyr.elf \

config/nrfconnect/app/overlay-usb_support.conf

@@ -22,4 +22,3 @@ CONFIG_USB_UART_CONSOLE=y
 
 CONFIG_UART_INTERRUPT_DRIVEN=y
 CONFIG_UART_LINE_CTRL=y
-CONFIG_UART_CONSOLE_ON_DEV_NAME="CDC_ACM_0"

config/nrfconnect/chip-module/Kconfig

@@ -32,6 +32,7 @@ config CHIP_NFC_COMMISSIONING
 config CHIP_OTA_REQUESTOR
 	bool
 	imply DFU_TARGET
+	imply BOOTLOADER_MCUBOOT
 	imply IMG_MANAGER
 	imply STREAM_FLASH
 	imply STREAM_FLASH_ERASE