Boolean parameters use circe to deserialize instead of akka-http, making values case-sensitive

This shouldn't be an issue for well-formed requests, but akka-http defines [multiple variants of what's valid](https://github.com/akka/akka-http/blob/3c3caa528144c2da4ff66ff1d2c08f4d382c7252/akka-http/src/main/scala/akka/http/scaladsl/unmarshalling/PredefinedFromStringUnmarshallers.scala#L36-L44) for Boolean parameters. By artificially constraining this, guardrail routes are not always drop-in replacements for existing akka-http implementations