move summary support check right after build

[crazy-max]

relates to https://github.com/docker/build-push-action/issues/1154

This moves summary support check right after build instead of post step and also gives better error message for GHES users instead of internal one used in actions-toolkit: https://github.com/docker/actions-toolkit/blob/7bd4fed6bcfc00fee61e9d307582e8351d7533f7/src/github.ts#L128