Add build step to deploy-wheels.yml that builds aarch64 wheels

[geoffreyblake]

Creates a binary wheel for manylinux2014_aarch64 using docker buildx
and dumps the resulting artifacts into the dist/ folder for upload to pypi.

Fixes #421

Changes proposed in this pull request:

• Adds buildx to the deploy-wheels.yml action, and creates the manylinux2014_aarch64 wheels in emulation
• Add a Dockerfile_aarch64 to the scripts/ directory that creates the wheels and copies out the artifacts.

[hugovk]

Thanks!

The wheels built:

• https://github.com/ultrajson/ultrajson/runs/1075773446?check_suite_focus=true

And deployed to TestPyPI:

• https://test.pypi.org/project/ujson/3.1.1.dev2/#files

Please could you test a deployed wheel (or wheels) install properly?

[geoffreyblake]

@hugovk , the wheels that were posted to https://test.pypi.org/project/ujson/3.1.1.dev2/#files install and load fine on AArch64. I tested on a Graviton2 machine running Centos8. When can a new release of ujson be expected?

[hugovk]

Thank you for testing!

I've just released UltraJSON 3.2.0 which has the new aarch64 wheels:

• https://pypi.org/project/ujson/3.2.0/#files

(btw I made a little adjustment to this PR so it builds Linux wheels in parallel: #423)

[geoffreyblake]

Thanks for the quick review/release!