Run tests on arm64 stack

[graphaelli]

Now available on 8.0.0-SNAPSHOT builds.

[kuisathaverat]

To run the ITs on ARM64 we need to run the APM Server on an ARM64 machine and run the ITs from another no ARM64 machine, otherwise, we need to port to ARM64 every Docker containers for the agent test applications.
Another option is to build an ARM64 Docker image for the APM server and run it with the ARM64 hypervisor.
https://www.docker.com/blog/multi-arch-images/
https://www.docker.com/blog/getting-started-with-docker-for-arm-on-linux/

[graphaelli]

I was expecting we'd pursue option 1, running just the Elastic Stack on arm, as we don't have specific plans to support agents on arm yet.