Switch links to Smithy v2 documentation (#2037)

## Motivation and Context

The latest documentation is Smithy v2. In most cases it's identical. As
far as I can tell, there are no links to items with breaking changes
between v1 and v2.

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Co-authored-by: Harry Barber <hlbarber@amazon.co.uk>
Co-authored-by: John DiSanti <jdisanti@amazon.com>