Default to gitlab-ee in zero downtime upgrade commands

What does this MR do and why?

Defaults to using to gitlab-ee in zero downtime upgrade command examples.

Zero-downtime upgrade Commands and instructions for gitlab-ce are still there, but gitlab-ee is used by default.

• Consistency - We default to using gitlab-ee package in all other command examples for installation and upgrades.
• Clarity - Support frequently links customers to the zero-downtime upgrade instructions, but customers only use gitlab-ee not gitlab-ce. Defaulting to gitlab-ee makes the examples copy/paste-able for customers, while keeping the notes about "replace gitlab-ee with gitlab-ce in examples above" ensures that CE users also find the instructions helpful and useful.

Screenshots or screen recordings

How to set up and validate locally

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.