Use docker offical build action

[AlexAxthelm]

using https://github.com/docker/build-push-action/ which enables multi-architecture builds and pushing to multiple registries, as well as other features available in buildx (such as build-time secrets)

[github-actions]

Docker image from this PR (70e2396) created

docker pull ghcr.io/rmi-pacta/workflow.pacta:pr12

[AlexAxthelm]

@cjyetman Please see #16 before approving. As this one stands, it leverages the build cache, but since the command to install the PACTA packages doesn't change, docker buildx build will gladly use the cached version, and not pick up changes from the other repos.

#16 splits the dockerfile into a multistage build, and leverages a feature of buildx to not cache particular stages (in this case, "installing PACTA"). I would highly recommend having that one follow on closely after this one, but it also depends on #15 and #14

[cjyetman]

@cjyetman Please see #16 before approving. As this one stands, it leverages the build cache, but since the command to install the PACTA packages doesn't change, docker buildx build will gladly use the cached version, and not pick up changes from the other repos.

#16 splits the dockerfile into a multistage build, and leverages a feature of buildx to not cache particular stages (in this case, "installing PACTA"). I would highly recommend having that one follow on closely after this one, but it also depends on #15 and #14

hmmm, yeah that would be pretty bad LOL.... but if you have a plan