Add attachments functionality to EventApi

[PestusAtSAG]

It would be create if we had the possibility to add attachment via EventApi,
the REST api provides that feature: see

[karol-c8y]

@PestusAtSAG could you open itrac ticket for that?

[vdiwe]

Can you pls add this API [https://cumulocity.com/api/core/10.18.0/#operation/postEventBinaryResource] in the SDK?

[karol-c8y]

@vdiwe @PestusAtSAG do you need other methods (GET/PUT/DELETE) of event binary api as well?