Query-tee improvements

[charleskorn]

What this PR does

This PR makes a number of small improvements to query-tee:

• it reduces the bucket factor of the native histogram metrics introduced in Querytee: Add metric to measure relative backend latency #7782 to give finer granularity
• it flips the meaning of the metrics introduced in Querytee: Add metric to measure relative backend latency #7782 to make them easier to reason about - I find these easier to think about this way around, as "secondary response time was 102% of preferred response time" or "secondary response time was 0.2s slower than preferred"
• it modifies backend_response_relative_duration_proportional to report the proportional difference, rather than just the proportional duration, as this gives values closer to 0 and therefore higher resolution

Each of these changes is in its own commit, and I suggest reviewing each commit separately.

Which issue(s) this PR fixes or relates to

(none)

Checklist

• Tests updated.
• [n/a] Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• [n/a] about-versioning.md updated with experimental features.

[jhesketh]

Yep, I agree this is easier to reason with, and since this hasn't been released yet I think it's fine to change at this point.

Only thing missing is docs/sources/mimir/manage/tools/query-tee.md needs updating please.

[jhesketh]

Thanks for adding docs :-)