This is a rebase of PR #10739 by @henryliu2014 on the current main
branch.
## Problem
pageserver: remove resident size from billing metrics
Fixes#10388
## Summary of changes
The following changes have been made to remove resident size from
billing metrics:
* removed the metric "resident_size" and related codes in
consumption_metrics/metrics.rs
* removed the item of the description of metric "resident_size" in
consumption_metrics.md
* refactored the metric "resident_size" related test case
Requested by: John Spray (john@neon.tech)
---------
Co-authored-by: liuheqing <hq.liu@qq.com>
Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: John Spray <john@neon.tech>