Support account-level entries in named-blob cleanup exclusion list

[zichengl]

Summary

Extends the named-blob cleanup exclusion list (added in #3286) to support account-level entries.

An entry in frontend.named.blob.cleanup.excluded.containers may now be:

• a bare accountName — exempts every container in that account, or
• accountName/containerName — exempts a single container (unchanged).

NamedBlobsCleanupRunner.isExcludedFromCleanup matches either form; the FrontendConfig doc is updated. Backward compatible — existing accountName/containerName entries are unchanged, and it remains durability-safe (retain-only: it can only ever cause the cleaner to delete less).

Motivation: some consumers need a whole account exempted — including containers created later — which the per-container form can't express.

Testing Done

Run under JDK 11:

• ./gradlew :ambry-frontend:test --tests com.github.ambry.frontend.NamedBlobsCleanupRunnerTest — 12/12 pass, including the new testAccountLevelExclusionSkipsEveryContainerInTheAccount: a bare account name skips every container in that account, while a container in a different account is still cleaned.
• ./gradlew :ambry-api:test --tests com.github.ambry.config.FrontendConfigTest — pass.

Risk

Additive and backward compatible; retain-only. Reversible by removing entries.

Notes

Design choice: this reuses the existing excluded.containers config (an entry is either accountName or accountName/containerName) rather than introducing a separate excluded.accounts property — minimal change, and downstream cfg2 bridges need no new field. Happy to switch to a dedicated account-list property if reviewers prefer the explicit split.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.75%. Comparing base (52ba813) to head (8efb17b).
⚠️ Report is 412 commits behind head on master.

Files with missing lines	Patch %	Lines
...github/ambry/frontend/NamedBlobsCleanupRunner.java	0.00%	3 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3289       +/-   ##
=============================================
- Coverage     64.24%   50.75%   -13.49%     
+ Complexity    10398     8682     -1716     
=============================================
  Files           840      938       +98     
  Lines         71755    80493     +8738     
  Branches       8611     9690     +1079     
=============================================
- Hits          46099    40855     -5244     
- Misses        23004    36241    +13237     
- Partials       2652     3397      +745     

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