Allow user to specify full image tags

Currently, we simply try to pull images that are prebuilt for the OS/Arch, but there is an edge-case where the image in question does not have a manifest for the OS/Arch in question. In those scenarios, we should be able to build them from source and use that locally built image.

Allow users to provide their own full image tags for server and client rather than just `:tag` suffixes. This way, they can use some locally built image.