wifi: Move Wi-Fi enterprise configs to a snippet

Instead of having an overlay move the Enterprise configurations to a
dedicated snippet so that it can be enabled with any sample.

Can be used along with Wi-Fi snippet e.g., `-S
"wifi-ipv4;wifi-enterprise"`.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>

snippets/wifi-enterprise/README.rst

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+.. _snippet-wifi-enterprise:
+
+Wi-Fi Enterprise Snippet (wifi-enterprise)
+##########################################
+
+.. code-block:: console
+
+   west build  -S wifi-enterprise [...]
+
+Can also be used along with the :ref:`snippet-wifi-ipv4` snippet.
+
+.. code-block:: console
+
+   west build  -S "wifi-enterprise,wifi-ipv4" [...]
+
+Overview
+********
+
+This snippet enables enterprise Wi-Fi support in supported networking samples.
+
+See :ref:`wifi_mgmt` for more information on the usage.
+
+Requirements
+************
+
+Hardware support for:
+
+- :kconfig:option:`CONFIG_WIFI`
+- :kconfig:option:`CONFIG_WIFI_USE_NATIVE_NETWORKING`
+- :kconfig:option:`CONFIG_WIFI_NM_WPA_SUPPLICANT`
+- :kconfig:option:`CONFIG_WIFI_NM_WPA_SUPPLICANT_CRYPTO_ENTERPRISE`

snippets/wifi-enterprise/snippet.yml

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+name: wifi-enterprise
+append:
+  EXTRA_CONF_FILE: wifi-enterprise.conf

snippets/wifi-enterprise/wifi-enterprise.conf

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+# Enable Wi-Fi enterprise mode
+CONFIG_WIFI_NM_WPA_SUPPLICANT_CRYPTO_ENTERPRISE=y
+# Use variable data size to reduce memory usage for small data packets
+CONFIG_NET_BUF_VARIABLE_DATA_SIZE=y
+# For TLS and X.509 processing MbedTLS needs large heap size and using separate heap
+# for MbedTLS gives us more control over the heap size.
+CONFIG_MBEDTLS_ENABLE_HEAP=y
+CONFIG_MBEDTLS_HEAP_SIZE=70000