Be able to specify both runtime and client versions

[timbrinded]

In order to perform upgrade tests, it would be useful to be able to specify separate runtime and client versions on a built chain.

For example:

• Acala Node, Client version: 2.4.0
• Acala Chain, Spec version: 2.3.3

Currently when using the generate CLI command, only the most uptodate chain data is generated for that docker image e.g. - image: acala/acala-node:2.4.0

[xlc]

What I did was to generate the spec with old image, and manually edit the output docker compose file to update the image.