Add docker manifest

[gracegoo-stripe]

Reviewers

r? @vcheung-stripe
cc @stripe/developer-products

Summary

In this PR, I included the arch in the image template. This lets us pull the correct version when specifying the image with the arch like so:

➜  stripe-cli git:(gracegoo-docker-manifest) ✗ docker images
REPOSITORY          TAG             IMAGE ID       CREATED          SIZE
stripe/stripe-cli   latest-amd64    3bdd1fd31953   11 seconds ago   29.1MB
stripe/stripe-cli   v1.13.1-amd64   3bdd1fd31953   11 seconds ago   29.1MB
stripe/stripe-cli   latest-arm64    42447b0cbc8a   14 seconds ago   28.2MB
stripe/stripe-cli   v1.13.1-arm64   42447b0cbc8a   14 seconds ago   28.2MB

➜  stripe-cli git:(gracegoo-docker-manifest) ✗ docker image inspect 3bdd1fd31953 | jq '.[].Architecture '
"amd64"
➜  stripe-cli git:(gracegoo-docker-manifest) ✗ docker image inspect 42447b0cbc8a | jq '.[].Architecture '
"arm64"

However, we were no longer publishing to the old image names (ex. stripe/stripe-cli:latest) so they still returned an image with an stripe v1.13.0 with only the ARM64 build.

This change adds a docker_manifests step to the goreleaser, which will allow us to publish a manifest list to the previous image names. In other words, stripe/stripe-cli:latest will now become a manifest list that contains multi-arch images, and docker will figure out what specific image to pull down.

About docker manifests: https://docs.docker.com/engine/reference/commandline/manifest/
Following guide here.

Testing

I was not able to find a way to test this locally. I could run a snapshot version of the releaser but it bypasses the publishing step which also happens to bypass manifest builds:

 goreleaser release -f .goreleaser/linux.yml --rm-dist --snapshot

Warning from the goreleaser docs:
"Unfortunately, the manifest tool needs the images to be pushed to create the manifest, that's why we both create and push it in the publishing phase."