Follow-up to #8900. Moves the gzip encoding and decoding config
validation off the Go `validateAndInjectDefaults` methods and onto
embedded Rego policies, injecting defaults and reporting value errors.
Each config registers its recognized options via
`config.RegisterConfigSpec` so unknown-option warnings live with the
owning struct. Field type validation stays in the Go decode step.
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Signed-off-by: Sebastian Spaink <sebastianspaink@gmail.com>
Sebastian Spaink