Add fields to sdk and category to let authors control display.

[Laren-AWS]

Add SDK and Category fields used by the publishing frontend to allow for customization of the display:

• sdk.display defines a string to display instead of the SDK key value so that a longer display string can be defined that's separate from the key.
• sdk.is_pseudo_sdk indicates whether the SDK is a true AWS SDK or something else. When true, the pseudo SDK is not included in the Code Library "by SDK" chapter.
• sdk.version.suppress_version_heading when true, suppresses the SDK version heading inside the tablist.
• category.synopsis_prefix defines strings for the synopsis prefix instead of the default "This code example shows how to".
• category.more_info defines a string that is used at the bottom of an example beneath the tablist that direct the reader to more information about the specific category of example.

These fields have already been incorporated into the backend ZonBook processor.

Testing

• Unit tests
• Root repo validation
• Internal builds

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