ARMv8 support.

[DzIGIBAUER]

As MTA now has server builds for ARMv8 it could be good to add option to specify it Dockerfile, like we specify MTA_SERVER_VERSION and MTA_SERVER_BUILD_NUMBER.
Wget request url would look like https://nightly.mtasa.com/multitheftauto_linux_${MTA_SERVER_ARCHITECTURE}-${MTA_SERVER_VERSION}-rc-${MTA_SERVER_BUILD_NUMBER}.tar.gz

x64 would be default.

It would allow running this docker image on Raspberry Pi's.

[4O4]

Hi, thanks for bringing this up. I'm not yet familiar with multiarch docker images but I will look into it and try to prepare an ARM build