Include minimum software versions in requirements docs

Problem to solve

https://docs.gitlab.com/ee/update/upgrading_from_source.html contains some outdated information. As discussed in #194206 (closed), we mention that the minimum required version of Go is 1.10, whereas we require 1.12.

Proposal

Documenting this similar to Ruby is worth a shot https://docs.gitlab.com/ee/install/requirements.html#ruby-versions.

We should also change the note here https://docs.gitlab.com/ee/update/upgrading_from_source.html#5-update-go to point to the requirements page so that we have only one place that we document this.

The more I read the upgrade page, the more similar issues I find :) We also mention a minimal version of Git or Node, which are not listed in the requirements page.