Revise cherry-pick page for CTRT

What does this MR do?

I had some time, and I have #293646 (closed) in my backlog requesting more plain language to be used in Git-related pages. I arbitrarily cherry-picked: https://docs.gitlab.com/ee/topics/git/cherry_picking.html

Notes for the reviewer:

• We used cherry pick on this page, but Git's documentation uses cherry-pick. I updated the instances here, and elsewhere, in the documentation to use the hyphenated version.
• I gardened in more information, especially around the concept of a SHA, because we didn't really tell a user what a SHA was or how to find it.
• Page is missing from the left nav. I've spun up gitlab-docs!2092 (merged) for that.

Related issues

Related to #293646 (closed)

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