Lock auto-deploy-app to specified version for each GitLab release

Problem

Currently Auto DevOps uses the latest version of auto-deploy-app. This means we cannot break backwards compatibility... ever.

We anticipate we will need to break backwards compatibility with issues like charts/auto-deploy-app#11 (moved).

Proposal

Specify the version of the auto-deploy-app to use in Auto DevOps script.

This will require us to bump the version whenever we need to upgrade, but it will give us control over which version of the chart GitLab uses.

TBC: Not sure what to do about previous versions of GitLab Auto DevOps which did not have the lock - will have to wait for several versions to pass, I guess.