nvs_flash: Modify the default NVS initialization API with internal nvs encryption

handling (only when nvs encryption is enabled)
    * NVS Encryption will now be turned on by default with flash encryption
    * Updated the flash encryption example to shocase NVS encryption
    along with information on how to configure and use NVS encryption
    * Updated respective test case
    * Added two partition tables for NVS encryption
     i) Table 1- Single factory app, no OTA, encrypted NVS
     ii) Table 2- Factory app, Two OTA, encrypted NVS

examples/system/ota/simple_ota_example/example_test.py

@@ -174,6 +174,9 @@ def test_examples_protocol_simple_ota_example_with_flash_encryption(env, extra_d
     binary_file = os.path.join(dut1.app.binary_path, "simple_ota.bin")
     bin_size = os.path.getsize(binary_file)
     ttfw_idf.log_performance("simple_ota_bin_size", "{}KB".format(bin_size // 1024))
+    # erase flash on the device
+    print("Erasing the flash in order to have an empty NVS key partiton")
+    dut1.erase_flash()
     # start test
     host_ip = get_my_ip()
     thread1 = Thread(target=start_https_server, args=(dut1.app.binary_path, host_ip, 8000))

examples/system/ota/simple_ota_example/sdkconfig.ci.flash_enc

@@ -18,3 +18,5 @@ CONFIG_EXAMPLE_ETH_MDIO_GPIO=18
 CONFIG_EXAMPLE_ETH_PHY_RST_GPIO=5
 CONFIG_EXAMPLE_ETH_PHY_ADDR=1
 CONFIG_EXAMPLE_CONNECT_IPV6=y
+# This is required for nvs encryption (which is enabled by default with flash encryption)
+CONFIG_PARTITION_TABLE_TWO_OTA_ENCRYPTED_NVS=y