Implement the Bluetooth current time service

Partial implementation, no notifications or time reference info for now.

CL: Implement the Bluetooth current time service

PUBLISHED_FROM=b6322789d9dab26ef2c8c886c7f4ad65948f90ef

Author: Deomid Ryabkov

include/esp32/esp32_bt.h

@@ -27,6 +27,7 @@ extern "C" {
 const uint16_t primary_service_uuid;
 const uint16_t char_decl_uuid;
 const uint16_t char_client_config_uuid;
+const uint8_t char_prop_read;
 const uint8_t char_prop_read_write;
 const uint8_t char_prop_read_notify;
 const uint8_t char_prop_write;

src/esp32/esp32_bt_gatts.c

@@ -90,6 +90,7 @@ static esp_gatt_if_t s_gatts_if;
 const uint16_t primary_service_uuid = ESP_GATT_UUID_PRI_SERVICE;
 const uint16_t char_decl_uuid = ESP_GATT_UUID_CHAR_DECLARE;
 const uint16_t char_client_config_uuid = ESP_GATT_UUID_CHAR_CLIENT_CONFIG;
+const uint8_t char_prop_read = ESP_GATT_CHAR_PROP_BIT_READ;
 const uint8_t char_prop_read_write =
     (ESP_GATT_CHAR_PROP_BIT_READ | ESP_GATT_CHAR_PROP_BIT_WRITE);
 const uint8_t char_prop_read_notify =