Add a be_like_time matcher and use it in specs

What does this MR do?

Introduces a be_like_time matcher and refactors existing code to use it

Are there points in the code the reviewer needs to double check?

A few sites use be_within(2.seconds) or 5.minutes - I didn't change those

Why was this MR needed?

A custom matcher helps to document that we need to compare times loosely, and keeps the fudge factor from being declared in multiple places.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Related to !6935 (merged)