feat: added testcase to check ota resumption if FE is enabled

This commit also added config option to set default buffer size for OTA.
This testcase mainly checks if OTA resumption fails if data written is
not 16 byte aligned when Flash Encryption is enabled.

examples/system/ota/advanced_https_ota/main/Kconfig.projbuild

@@ -53,4 +53,11 @@ menu "Example Configuration"
             This option allows one to configure the OTA process to resume downloading the OTA image
             from where it left off in case of an error or reboot.
 
+    config EXAMPLE_OTA_BUF_SIZE
+        int "OTA buffer size"
+        default 1024
+        range 1024 65536
+        help
+            Buffer size for OTA data transfers in bytes.
+
 endmenu

examples/system/ota/advanced_https_ota/main/advanced_https_ota_example.c

@@ -227,6 +227,7 @@ void advanced_ota_example_task(void *pvParameter)
 #ifdef CONFIG_EXAMPLE_ENABLE_PARTIAL_HTTP_DOWNLOAD
         .save_client_session = true,
 #endif
+        .buffer_size = CONFIG_EXAMPLE_OTA_BUF_SIZE,
     };
 
 #ifdef CONFIG_EXAMPLE_FIRMWARE_UPGRADE_URL_FROM_STDIN