Use "terminus" instead of Pantheon CLI in Pantheon WebOps Certification

[jkudish]

Summary

WebOps Certification: Chapter 5: CMS Infrastructure (backups section) - Since we use "terminus" throughout the rest of the certification docs, it can appear confusing to use "Pantheon CLI" here. As I was reading it, I had to make sure this was referring to terminus by checking the URL it was pointed to.

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Post Launch

Do not remove - To be completed by the docs team upon merge:

• [ ] Redirect /old-path/ => /new-path/ (if applicable)
• [ ] Include/exclude pages ^ respectively within docs search service provider (if applicable)
• [ ] For Heroes - add a props post to the discussion board.
• [ ] Remove from the project board