set Tokaido to use pinned image tags, rather than 'edge' or 'stable'

[ironmike-au]

With this PR, Tokaido will use specific Docker image tags that correspond to that Tokaido release.

For example, Tokaido 1.11.0 will use Docker Images tagged 1.11.0.

We will still have the concept of "edge" and "stable" releases, as matched against which version of Tokaido is running in the Ironstar prod and non-prod clusters.

This change enables us to remove the docker-pull functionality which takes unnecessary time during up, and will also enable us to offer more consistency between Tokaido versions.

[jimmycann]

A positive change, but could this break people when upgrading Tokaido? Could end up being an unintended deterrent. We may need to consider the ability for our users to upgrade Tokaido and their containers asynchronously, without having to use custom compose file.

[ironmike-au]

A positive change, but could this break people when upgrading Tokaido? Could end up being an unintended deterrent. We may need to consider the ability for our users to upgrade Tokaido and their containers asynchronously, without having to use custom compose file.

I'd like to move us to a google cloud model of auto-updating, where each time the user runs, if there's an update, they get prompted to instal lit there and then. It's much quicker and easier than using homebrew, which it turns out most people don't update at all.

This should encourage people on to newer versions. At the same time, we can look at making it easy to roll back to previous container versions.