Publish docs for the 3 most recent major versions instead of 3 most recent minor versions

Blocked by gitlab#16610 (closed)

---

Currently, on docs.gitlab.com we publish docs for GitLab.com and the previous three minor releases.

Could we change this to GitLab.com and the last minor release for currently supported major releases? At the time of posting, it will look like this:

• GitLab.com
• 12.2
• 11.11
• 10.8

Pros:

• Aligns with our policy to support the three most recent major versions
• Easier for users, customers and GitLab Support to refer and link to relevant documentation for self-managed instances

Cons:

• We'd need to be more mindful to document differences between minor versions as the latest minor version becomes the single source of truth/reference