misleading ENV NAMES

ENV variables have misleading names in that file

https://github.com/jembi/openhim-console/blob/b403f987be62781a2ecf3a9b0a1ac9845a353109/app/config/default-env.json#L6C18-L6C42

I proposed those changes 

OPENHIM_CORE_MEDIATOR_HOSTNAME -> OPENHIM_CORE_HOSTNAME 
OPENHIM_CONSOLE_HOSTPATH -> OPENHIM_CORE_API_HOSTPATH
OPENHIM_MEDIATOR_API_PORT -> OPENHIM_CORE_API_PORT

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