[cherry-pick] Cache image list with digest key

[stonezdj]

fixes #19429

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Comprehensive Summary of your change

Issue being fixed

Fixes #(issue)

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• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (b622d4a) 67.42% compared to head (394fe30) 67.42%.
Report is 2 commits behind head on release-2.9.0.

Additional details and impacted files

@@                Coverage Diff                @@
##           release-2.9.0   #19837      +/-   ##
=================================================
- Coverage          67.42%   67.42%   -0.01%     
=================================================
  Files                993      993              
  Lines             108932   108938       +6     
  Branches            2752     2752              
=================================================
+ Hits               73444    73448       +4     
  Misses             31534    31534              
- Partials            3954     3956       +2     

Flag	Coverage Δ
unittests	67.42% <33.33%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/controller/proxy/controller.go	15.59% <50.00%> (-0.26%)	⬇️
src/controller/proxy/manifestcache.go	26.27% <0.00%> (-0.59%)	⬇️

... and 5 files with indirect coverage changes

[wy65701436]

lgtm