example: Synchronize includes in BLE walkthrough

Previously, the includes in the initial walkthrough section were
different from the actual ones used includes in the code example.
Moreover, if one was following the walkthrough and only taking
inspiration from there rather than the code itself, with these includes,
the code wouldn't compile. Synchronize the source code file with the
walkthrough in this regard.

Signed-off-by: František Nečas <frantisek.necas@protonmail.com>

examples/bluetooth/bluedroid/ble/gatt_server/tutorial/Gatt_Server_Example_Walkthrough.md

@@ -18,17 +18,17 @@ First, let’s take a look at the includes:
 #include "esp_system.h"
 #include "esp_log.h"
 #include "nvs_flash.h"
-#include "bt.h"
-#include "bta_api.h"
+#include "esp_bt.h"
 #include "esp_gap_ble_api.h"
 #include "esp_gatts_api.h"
 #include "esp_bt_defs.h"
 #include "esp_bt_main.h"
+#include "esp_gatt_common_api.h"
 #include "sdkconfig.h"
 ```
-These includes are required for the FreeRTOS and underlaying system components to run, including the logging functionality and a library to store data in non-volatile flash memory. We are interested in `"bt.h"`, `"esp_bt_main.h"`, `"esp_gap_ble_api.h"` and `"esp_gatts_api.h"`, which expose the BLE APIs required to implement this example.
+These includes are required for the FreeRTOS and underlaying system components to run, including the logging functionality and a library to store data in non-volatile flash memory. We are interested in `"esp_bt.h"`, `"esp_bt_main.h"`, `"esp_gap_ble_api.h"` and `"esp_gatts_api.h"`, which expose the BLE APIs required to implement this example.
 
-* `bt.h`: implements BT controller and VHCI configuration procedures from the host side.
+* `esp_bt.h`: implements BT controller and VHCI configuration procedures from the host side.
 * `esp_bt_main.h`: implements initialization and enabling of the Bluedroid stack.
 * `esp_gap_ble_api.h`: implements GAP configuration, such as advertising and connection parameters.
 * `esp_gatts_api.h`: implements GATT configuration, such as creating services and characteristics.