use GoReleaser to build and push container images

we've (w/@dentrax) just noticed that this project currently uses GoReleaser to make a new release, and the `buildx` tool to build and push container images, so, we can use GoReleaser to do the same for container images. By doing so, we can remove an additional step in the GitHub Actions workflow for building/pushing container images, also, we can sign our container images or binaries with cosign too.

Feel free to assign this to us, if you agree with this idea, we would love to work on this 🥳