Mark fields optional or required in StreamConfiguration

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In the StreamConfiguration section, the description field says:

An optinal string to describe the properties of the stream. This is useful in multi stream systems to identify the stream for human actors. The transmitter may truncate the string beyond allowed max length.

This is the only StreamConfiguration field that says anything about whether the field is optional or not. We should either:

1. Infer from this that all of the other fields must be required
2. Be explicit about which fields are required/optional