CNDB-12774: change CompactionObserver#onCompleted to include failure exception

[jasonstack]

https://jenkins-stargazer.aws.dsinternal.org/view/cc-builds/job/ds-cassandra-publish-j11/1293/

[github-actions]

Checklist before you submit for review

• Make sure there is a PR in the CNDB project updating the Converged Cassandra version
• Use NoSpamLogger for log lines that may appear frequently in the logs
• Verify test results on Butler
• Test coverage for new/modified code is > 80%
• Proper code formatting
• Proper title for each commit staring with the project-issue number, like CNDB-1234
• Each commit has a meaningful description
• Each commit is not very long and contains related changes
• Renames, moves and reformatting are in distinct commits

[eolivelli]

makes sense

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
91.7% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cassci-bot]

❌ Build ds-cassandra-pr-gate/PR-1573 rejected by Butler

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2 new test failure(s) in 3 builds
See build details here

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Found 2 new test failures

Test	Explanation	Branch history	Upstream history
...>,wide=true,scenario=POST_BUILD_QUERY]	regression	🔴🔵🔵	🔵🔵🔵🔵🔵🔵🔵
o.a.c.u.b.BinLogTest.testTruncationReleasesLogS...	regression	🔴🔵🔴	🔵🔵🔵🔵🔵🔵🔵

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Found 8 known test failures