Improve Go language upgrade process documentation

What does this MR do and why?

Updates our Go language upgrade process documentation per the FCL process.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related gitlab-org/distribution/team-tasks#925 (closed)

Closes omnibus-gitlab#6416 (closed)