Support X-Cumulocity-Processing-Mode

[haraldmeyer]

Cumulocity allows to define data to be received in transient modes so that it will not be stored in the database but only be made available for real-time processing. This is controlled via the X-Cumulocity-Processing-Mode.

Potential options:

• allow device codecs to define the processing mode of data sent in C8YData
• Make this a general per-device option that allows users to define if data for a specific device should be persisted or not.