Assign proper emails for "Contact Partner" dialog

[djang0402]

Summary

Web UI has "Contact Partner" button to open a dialog for sending some messages to the vendor. But we cannot configure email addresses, which receive the messages through the dialog.

Why do we need this?

Our customer wrote messages through the dialog, but the messages was sent to TTN. End-device definition would need elements to configure emails receiving messages through the dialog.

What is already there? What do you see now?

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What is missing? What do you want to see?

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How do you propose to implement this?

Adding emails elements to the end-device.yaml schema. But you should have better idea than me. :)

Can you do this yourself and submit a Pull Request?

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