add client disconnect reason text in events

[razvanphp]

This helps as well to display the reason on libs that link logging based on Events only.

https://github.com/matth-x/MicroOcpp/blob/0455ec05aabdb3475cbd2dedee430acc51b155c7/src/MicroOcpp/Core/Connection.cpp#L71-L75

[razvanphp]

Logs in MicroOcpp look like this now:

[19:03:37][OCPP] [MO] info (Connection.cpp:75):
[19:03:37][OCPP] Disconnected: Connection lost
[...]
[19:03:45][OCPP] [MO] info (Connection.cpp:75):
[19:03:45][OCPP] Disconnected: TCP connection cleanup
[...]
[02:00:13][OCPP] [MO] info (Connection.cpp:75):
[02:00:13][OCPP] Disconnected: WebSocket handshake failed - HTTP 401
[02:00:19][OCPP] [MO] info (Connection.cpp:75):
[02:00:19][OCPP] Disconnected: WebSocket handshake failed - HTTP 401

Before, one could not see / understand what the problem is.