provide apt package, docker image for linux/arm64 hosts (18.1.0)

Start by inspecting the Dockerfile and the package/image build and publishing configuration for stellar-core, then check how apt.stellar.org currently publishes architecture metadata. Done means linux/arm64 variants are available for both the Docker image and apt package, so arm64 Ubuntu builds can resolve the package without the reported architecture warning.

Description

Explain in detail the additional functionality you would like to see in stellar-core.

Provide linux/arm64 architecture builds of the apt package and the stellar-core docker images. currently there are only linux/amd64 versions provided.

Explain why this feature is important

For anyone running macbooks with the Apple silicon chips, which are on arm64 ISAs, when running stellar-core docker images, Docker splashes up Warning messages:
WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested

the docker image does appear to still run afterwards though, but wanted to mention this warning output for visibility in case may accrue problems over time.

Also, can't build other Docker images locally that reference the stellar-core apt package from apt.stellar.org , during the Docker build output, after adding apt.stellar.org to apt, apt-get update it fails with:

N: Skipping acquire of configured file 'unstable/binary-arm64/Packages' as repository 'https://apt.stellar.org focal InRelease' doesn't support architecture 'arm64'
N: Skipping acquire of configured file 'stable/binary-arm64/Packages' as repository 'https://apt.stellar.org focal InRelease' doesn't support architecture 'arm64'

apt repo has linux/amd64 binaries, but the Dockerfile build for ubuntu base image is defaulting to host machine arch of linux/arm64, and not finding pkg.

Describe the solution you'd like

would. be convenience if linux/arm64 arch versions were provided for stellar-core docker image and apt pkg.

Describe alternatives you've considered

Maybe brief blurb in Documentation to say ignore WARNING: The requested image's platform does not match ... if running the docker image on newer Apple M1 macs.