:latest tag management

[euank]

I believe in the past this repository had a manually triggered Jenkins job which would mirror master to latest as a sort of 'promotion' / 'release'.
Do you recall if that was the case and if there were any more details there @colhom?

We should likely set something like that up agian since latest is quite out of date at this point.

Note that we shouldn't mirror master quite yet since #15 should be resolved first to avoid regressions on latest.

[whereisaaron]

When an image it promoted/release to 'latest', can it also be tagged with a version? With version tags, users can pull version tagged images that won't be subject to potentially breaking changes like #15.

I suggest tagging them with the version of awscli they contain, since this the only purpose of the container. But really, any version tag to maintain an invariant image would be enormously helpful.

[euank]

I agree that immutable versioned tags should be published as well.