[ChargePoint] Switch from private to protected

This could be a quality of life as there is no need to directly inherit from IChargePoint only, and thus reimplement what has been done in ChargePoint when only 1 or 2 methods need to be override.

As ChargePoint implement most methods, it is easier to inherit from ChargePoint especially when there are changes between releases.

Author: thomas-brunel

src/chargepoint/ChargePoint.h

@@ -243,7 +243,7 @@ class ChargePoint : public IChargePoint,
     /** @copydoc void IConfigChangedListener::configurationValueChanged(const std::string&) */
     void configurationValueChanged(const std::string& key) override;
 
-  private:
+  protected:
     /** @brief Stack configuration */
     const ocpp::config::IChargePointConfig& m_stack_config;
     /** @brief Standard OCPP configuration */