PR #431115 changed extraStructuredConfig to structuredExtraConfig to
follow the deprecation warning about `extraConfig`. However,
`extraStructuredConfig` was mentioned in several places in the docs that
weren't addressed. Also, using this would silently fail since the code
in question would still accept the old key.
This patch updates the docs accordingly and throws an error if the
code-path is reached and `extraStructuredConfig` is being used.
dccb264578