add metric for collecting storages (backport #17527)

[mergify]

This is an automatic backport of pull request #17527 done by Mergify.
Cherry-pick of 72bb271 has failed:

On branch mergify/bp/v1.7/pr-17527
Your branch is up to date with 'origin/v1.7'.

You are currently cherry-picking commit 72bb271a9.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   runtime/src/accounts_hash.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   runtime/src/accounts_db.rs
	both modified:   runtime/src/snapshot_utils.rs

To fix up this pull request, you can check it out locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

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[codecov]

Codecov Report

Merging #17675 (6bf91d4) into v1.7 (04fbf73) will increase coverage by 0.0%.
The diff coverage is 94.7%.

@@           Coverage Diff           @@
##             v1.7   #17675   +/-   ##
=======================================
  Coverage    82.5%    82.5%           
=======================================
  Files         428      428           
  Lines      119472   119489   +17     
=======================================
+ Hits        98681    98696   +15     
- Misses      20791    20793    +2