HCD-147: Add createsystemkey subcommand to nodetool

[szymon-miezal]

This commit extends nodetool with createsystemkey command.
The motivation is to allow users to create encryption keys that can
be used for flat-file based encryption in TDE.

CNDB PR: https://github.com/riptano/cndb/pull/14205.

[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
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
90.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cassci-bot]

✔️ Build ds-cassandra-pr-gate/PR-1759 approved by Butler

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Approved by Butler
See build details here

[bereng]

IIUC your CNDB PR is not poiniting at any SHA in this CC PR?