CNDB-12346: Fix reporting enqueue time for stage tasks (#1490)

[jakubzytka]

Enqueue start time will now be correctly measured for every API for task
execution

What is the issue

Enqueue start times are measured at a wrong moment for some APIs.

What does this PR fix and why was it fixed

We now measure the enqueue start time as a time of entry to each task
execution API.
It was fixed so that we see the correct enqueue times in metrics

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

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cassci-bot]

❌ Build ds-cassandra-pr-gate/PR-1493 rejected by Butler

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8 new test failure(s) in 1 builds
See build details here

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Found 8 new test failures

Test	Explanation	Branch history	Upstream history
t.TestCqlshUnicode.test_unicode_identifier	regression	🔴
t.TestCqlshUnicode.test_unicode_value_round_trip	regression	🔴
...adRepairGuarantees.test_atomic_writes[blocking]	regression	🔴
...ToolEnableDisableBinaryTest.testMaybeChangeDocs	regression	🔴
...ist,wide=false,scenario=MEMTABLE_QUERY]	regression	🔴
...t.testKDTreePostingsQueryMetricsWithSingleIndex	regression	🔴
...m.TrieMemtableMetricsTest.testContentionMetrics	regression	🔴
o.a.c.u.b.BinLogTest.testTruncationReleasesLogS...	regression	🔴

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No known test failures found