Make the chart versions match the ones of GitLab itself

Proposal

It would be great if the chart version matched GitLab itself!

Pros

1. Easier to understand which Chart version applies to what GitLab version
2. Unified versioning for the docs site. The version number is universal and comes before the various products (docs.gitlab.com/11.8/<product>). If the chart has different versioning, we'll need to find a way to 1) pull that in the respective Docker image that contains the docs version, and 2) show the users on the site which version they're browsing.

Cons

1. Feature parity. Not all GitLab features are available in the current charts. I guess this is the primary reason why we haven't changed the versioning yet.
2. Breaking changes to large / key components could require major version updates significantly out of line with major versions of GitLab
3. ?