Introduce CF param for verssion of config

[adamnfish]

Previously the version was hard-coded to "master" and fetched directly out of Github. This meant that if a new instance was brought up after the master branch had changed, the instance would be running different
config to the rest of the cluster. Generally this would break the cluster.

[satterly]

👍 from me ... @TBonnin any objections?

[TBonnin]

It is better for sure but still easy to shoot yourself in the foot by using the default 'master' value.

I wonder if we should find a way to set this commit hash automatically. For instance a post-merge hook that would update the commit ID to the current head.

[adamnfish]

I'm sure a post-merge hook wouldn't do what people expect. Let's chat about it IRL, after stand up?

[johnduffell]

sounds better to me, although getting it from the build output would make more sense than from git directly, I'm not a big fan of automatically writing back to git if that's what the suggestion is