Support for container version management / rollback via CLI

[joshjohanning]

For repeatability of migration runs, someone might want to downgrade a particular backend container image.

Could be something like gh actions-importer upgrade -v 1.1.16794 or gh actions-importer downgrade 1.1.16794.

Manual workaround to use a specific container version:

docker pull ghcr.io/actions-importer/cli:1.1.16794 # pull specific version of container
docker tag ghcr.io/actions-importer/cli:1.1.16794 ghcr.io/actions-importer/cli:latest # re-tag as latest