snippets: Add nus-console snippet

Allowing to be applied on various samples to enable UART over Bluetooth
LE NUS without added complexity.
Tested with nrf52840dk/nrf52840 on the following samples:
- samples/subsys/console/echo.
- samples/subsys/console/getchar.
- samples/subsys/console/getline.
- samples/subsys/logging/logger.

Signed-off-by: Luis Ubieda <luisf@croxel.com>

snippets/nus-console/README.rst

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+.. _snippet-nus-console:
+
+NUS Console Snippet (nus-console)
+########################################
+
+.. code-block:: console
+
+   west build -S nus-console [...]
+
+Overview
+********
+
+This snippet redirects serial console output to a UART over NUS (Bluetooth LE) instance.
+The Bluetooth Serial device used shall be configured using :ref:`devicetree`.
+
+Requirements
+************
+
+Hardware support for:
+
+- :kconfig:option:`CONFIG_BT`
+- :kconfig:option:`CONFIG_BT_PERIPHERAL`
+- :kconfig:option:`CONFIG_BT_NUS`
+- :kconfig:option:`CONFIG_SERIAL`
+- :kconfig:option:`CONFIG_CONSOLE`
+- :kconfig:option:`CONFIG_UART_CONSOLE`
+
+A devicetree node with node label ``bt_nus_console_uart`` that points to an enabled
+device node with nus-uart support. This should look roughly like this in
+:ref:`your devicetree <get-devicetree-outputs>`:
+
+.. code-block:: DTS
+
+   bt_nus_console_uart: bt_nus_console_uart {
+      compatible = "zephyr,nus-uart";
+        /* ... */
+   };

snippets/nus-console/nus-console.conf

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+CONFIG_SERIAL=y
+CONFIG_CONSOLE=y
+CONFIG_UART_CONSOLE=y
+
+CONFIG_BT=y
+CONFIG_BT_PERIPHERAL=y
+CONFIG_BT_NUS=y
+CONFIG_UART_BT=y
+CONFIG_BT_NUS_AUTO_START_BLUETOOTH=y
+
+# Bluetooth optimizations to allow larger data packets.
+CONFIG_BT_RX_STACK_SIZE=2048
+CONFIG_BT_L2CAP_TX_MTU=512
+CONFIG_BT_BUF_ACL_RX_SIZE=502
+CONFIG_BT_BUF_ACL_TX_SIZE=502
+CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

snippets/nus-console/nus-console.overlay

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+/*
+ * Copyright (c) 2024 Croxel, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	chosen {
+		zephyr,console = &bt_nus_console_uart;
+	};
+
+	bt_nus_console_uart: bt_nus_console_uart {
+		compatible = "zephyr,nus-uart";
+		rx-fifo-size = <1024>;
+		tx-fifo-size = <1024>;
+	};
+};

snippets/nus-console/snippet.yml

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+name: nus-console
+append:
+  EXTRA_CONF_FILE: nus-console.conf
+  EXTRA_DTC_OVERLAY_FILE: nus-console.overlay