Follow-up from "Expose Issues Completed under GraphQL flow metrics"

This is a follow-up issue from !119423 (merged)

Items to address:

• Update the documentation for the timestamp filters: !119423 (comment 1377835210) 👉 Done in !119915 (merged)
• Move the EE specific metric tests/shared examples to the EE folder (lead time, etc.). 👉 !121969 (merged)
• See if we can use a shared context for these: !119423 (comment 1377663516) Moved to #415306 (closed)

These are mostly optional IMHO, if we see that it's not worth the effort or it wouldn't improve things significantly, feel free to close the issue.

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The following discussion from !119423 (merged) should be addressed:

• @cablett started a discussion: (+1 comment)

  To the reviewer: I notice LeadTime is EE only, and yet the specs appear in this non-EE support file. Should we move all of the EE-only ones to ee/spec/support? These classes are only called from EE classes but I think it might be better they live in the right place.