Add support in Pekko interpreter for status codes >=600

[gkepka]

Pekko supports registering custom status codes with values >=600. Currently, if an endpoint returns such a status code, the Pekko interpreter will crash due to the call to the two argument version of StatusCodes.custom. This PR adds possibility of registering Pekko custom status codes using PekkoHttpServerOptions fixes that behavior by using the five parameter version of the method.

[gkepka]

This is obviously not correct, but I don't know which version to use in an example for a feature that has not been released yet.

[adamw]

Unfortunately examples of new features have to be commented out until there's a release

[adamw]

As I understand you need to call the StatusCodes.custom(800, "Custom reason", "Custom message", isSuccess = false, allowsEntity = true) constructor - maybe we can simply always do that, if the status code is not found? Always allowing an entity etc. - I don't think that information is used anywhere anyhow, as it's simply used to send the response? and these flags don't seem to influence that process

[gkepka]

For my use case it will be enough. I haven't checked the Pekko HTTP internals very carefully, but judging from a glance parameters like reason or defaultMessage seem to be used for handling responses only. It should be safe to leave them empty.

[adamw]

Maybe add a test? :)

[adamw]

PekkoHttpServerTest might be a good place

[adamw]

Thanks :)