[synthetics] Update docs to reflect the changes to `expect` #3297

Merged

colleenmcginnis merged 3 commits intoelastic:mainfrom colleenmcginnis:issue-3206

Oct 19, 2023

+8-38

Commits on Oct 18, 2023

Commits on Oct 19, 2023

clarify what's not supported
colleenmcginnis
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