CNDB-18108 Add system property to disable UDFs and skip SecurityManager installation (#2452)

[djatnieks]

Introduces the -Dcassandra.disable_user_defined_functions system property:

• When set to true, UDF creation and execution are blocked, and ThreadAwareSecurityManager installation is skipped
• Takes precedence over the YAML enable_user_defined_functions setting
• Defaults to false to maintain backward compatibility
• SecurityManager installation is skipped because it is only used for sandboxing UDFs

[github-actions]

Checklist before you submit for review

• This PR adheres to the Definition of Done
• Make sure there is a PR and ticket 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 IBM copyright header instead of the Apache License one (no DataStax copyright any longer)

[plpesvc-ds]

❌ Build ds-cassandra-pr-gate/PR-2486 rejected by Butler

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3 regressions found
See build details here

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Found 3 new test failures

Test	Explanation	Runs	Upstream
o.a.c.index.sai.cql.VectorCompaction100dTest.testCompactionWithEnoughRowsForPQAndDeleteARow[version=ec enableNVQ=false] ()	NEW	🔴	0 / 30
o.a.c.index.sai.cql.VectorKeyRestrictedOnPartitionTest.partitionRestrictedTest[dc false] (compression)	REGRESSION	🔴	0 / 30
o.a.c.index.sai.cql.VectorSiftSmallTest.testRerankKZeroOrderMatchesFullPrecisionSimilarity[ec true] ()	NEW	🔴	0 / 30

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No known test failures found