feat: linux/arm64 multi-platform support

[flotwig]

Closes #431
Closes cypress-io/cypress#22167

This PR introduces beta support for linux/arm64 images, mainly to enable M1 users to run Cypress docker images locally.

The only known limitation is that none of Chrome, Firefox, or Edge officially support linux-arm64 yet - so this means none of the browsers or included images will have browsers on linux/arm64. Users will have to use --browser electron or obtain their own arm64 browser binaries.

As arm64 binaries become available, they will be added to these images. See #695 for details.

For now, users will see this warning on arm64:

This PR also:

• Moves our AWS ECR image generation to Circle, dropping the need for AWS BuildSpec
• Switches to docker buildx in CI
• Adds snapshot tests for "generate-config" (1418 lines of this diff are snapshots)

@admah we still need to make a decision on how far back we want to go with updating older images to have linux/arm64 builds - right now, I'm thinking we'll just do the latest included image, and the browsers and base images upon which that relies.

Pre-merge:

• Remove Circle environment variables, add Docker Hub and AWS ECR creds to Circle Context

Post-merge:

• Release linux/arm64 builds for select images on ECR and Hub

[flotwig]

will this also close out #694? Did you remove all references to cly?

@admah I just removed the final mention 👍 This PR can replace #694 now

[admah]

Looks good to me! Great work.