[fix][ml]Expose ledger timestamp

[dao-jun]

Fixes #22312

Motivation

Modifications

see #22312

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[lhotari]

LGTM

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 73.74%. Comparing base (bbc6224) to head (44cd4a0).
Report is 85 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #22338      +/-   ##
============================================
+ Coverage     73.57%   73.74%   +0.17%     
+ Complexity    32624    32324     -300     
============================================
  Files          1877     1886       +9     
  Lines        139502   139439      -63     
  Branches      15299    15287      -12     
============================================
+ Hits         102638   102832     +194     
+ Misses        28908    28645     -263     
- Partials       7956     7962       +6     

Flag	Coverage Δ
inttests	26.93% <0.00%> (+2.35%)	⬆️
systests	24.48% <0.00%> (+0.15%)	⬆️
unittests	72.99% <0.00%> (+0.14%)	⬆️

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

Files	Coverage Δ
...kkeeper/mledger/impl/ManagedLedgerFactoryImpl.java	81.02% <0.00%> (-0.36%)	⬇️

... and 134 files with indirect coverage changes