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/security/flash_encryption/example_test.py

@@ -52,7 +52,9 @@ def test_examples_security_flash_encryption(env, extra_data):
         'with esp_partition_read',
         plain_hex_str,
         'with spi_flash_read',
-        expected_str
+        expected_str,
+        # The status of NVS encryption for the "nvs" partition
+        'NVS partition "nvs" is encrypted.'
     ]
     for line in lines:
         dut.expect(line, timeout=2)