Add ISO 11783 message types for Field, Farm, and Customer

[saschadoemer]

No description provided.

[Copilot]

Pull Request Overview

This PR adds support for three new ISO 11783 message types in the ContentMessageType enum to handle farm master data communication.

• Added ISO_11783_FIELD, ISO_11783_FARM, and ISO_11783_CUSTOMER message types
• Each new type includes both content type identifier and protobuf message class specification
• Removed outdated FIXME comment about spec availability

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