OCPP 2.1 support

[nick-jones]

The current schema defines messageType as the following enum: ["CALL", "CALLRESULT", "CALLERROR"]

However, the 2.1 OCPP-J spec introduced 2 additional message types: CALLRESULTERROR and SEND. I assume these should be covered if a goal is for broad version support?

[juherr]

Good catch — yes, OCPP 2.1 should be representable by the trace format.

We should add CALLRESULTERROR and SEND to messageType and review the related conformance/correlation rules as well, rather than only extending the enum.