feat(ble): add behavior to disconnect from BLE profile

Adds new functionality and a behavior to disconnect an active BLE connection.
The motivation for this is that for some devices like phones, the presence of an
active BLE connection results in the onscreen keyboard being selected.

app/src/behaviors/behavior_bt.c

@@ -31,6 +31,8 @@ static int on_keymap_binding_pressed(struct zmk_behavior_binding *binding,
         return zmk_ble_prof_prev();
     case BT_SEL_CMD:
         return zmk_ble_prof_select(binding->param2);
+    case BT_DISC_CMD:
+        return zmk_ble_prof_disconnect(binding->param2);
     default:
         LOG_ERR("Unknown BT command: %d", binding->param1);
     }