Provide a mechanism to pin working apko release version

[mbrancato]

Description

Given recent build issues like the following, it would be nice to have the apko release version be an input to this action to pin it to a working version.

• unable to lock packages to a consistent version: map[myapp@local:[ (amd64)]] chainguard-dev/apko#1471
• apko-publish@main fails with "Error: failed to build image components: generating index SBOM: generating spdx sbom: unable to render index sbom, no architecture images found" #158

Instead of pulling the very large wolfi-dev/sdk it could use wolfi-dev/alpine-base and pull apko from the GitHub release artifact instead. This would allow pinning to a version without a 400+MB container image needed for a few basic shell commands.