CNDB-13624: Silence snakeyaml warnings in test-cdc by removing duplicate cdc_enabled key in base yaml

[jkni]

What is the issue

#1563 upgraded our version of snakeyaml. This new version logs when duplicate keys are found. The test-cdc target concatenates a CDC-specific yaml to the base yaml. Both contain entries for the cdc_enabled key, causing tests that load this yaml to log the warning. This causes CDC CI failures.

What does this PR fix and why was it fixed

This PR removes the cdc_enabled entry in the base yaml, as it's the same as the default. This is consistent with how we handle other default keys that might be duplicated across multiple yaml fragments in the test commands.

[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
• All new files should contain the DataStax copyright header instead of the Apache License one

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud

[cassci-bot]

✔️ Build ds-cassandra-pr-gate/PR-1680 approved by Butler

---

Approved by Butler
See build details here

[ekaterinadimitrova2]

+1
commitlog_compression also exists in the base yaml, but it is commented out so it does not produce any warnings.

This new version logs when duplicate keys are found.

It was high time, this was a reason for confusion and some bugs. Half people actively use it, half people have no clue overriding exists. That is how CASSANDRA-17379 was born. From Apache Cassandra 4.1+:
[CASSANDRA-17379](https://issues.apache.org/jira/browse/CASSANDRA-17379) was opened to improve the user experience and deprecate the overloading. By default, we refuse starting Cassandra with a config containing both old and new config keys for the same parameter. Start Cassandra with -Dcassandra.allow_new_old_config_keys=true to override. For historical reasons duplicate config keys in cassandra.yaml are allowed by default, start Cassandra with -Dcassandra.allow_duplicate_config_keys=false to disallow this. Please note that key_cache_save_period, row_cache_save_period, counter_cache_save_period will be affected only by -Dcassandra.allow_duplicate_config_keys.

[jkni]

Thanks for the review! I briefly considered disabling these warnings to revert to the old behavior, but I think they're a positive change.