Fleet-Server for arm64

For all you aarch64/arm64 loving people out there, I ported fleet-server to arm64.

If you are running a raspberry pi elastic cluster and are trying out the bleeding edge releases, the last 7.13.x release left you out in the cold. Fleet-Server has not been released officially for arm64.

Until then, feel free to use my containerized version for arm64.

https://hub.docker.com/repository/docker/fgierlinger/fleet-server