Add Support For Hardcore Bedrock

[Austin-Higgins]

Enhancement Type

Not sure

Describe the enhancement

Latest branch does not have the environmental variable config for HARDCORE parameter. This is something I can help add if needed. I would really like to use this feature. :)

[itzg]

Yeah, that would be great if you could add a property mapping for that in https://github.com/itzg/docker-minecraft-bedrock-server/blob/master/property-definitions.json