Introduce a MetricsFactory which can be used to produce metrics objects at the Table and Keyspace level, and which is customizable

[scottfines]

This ensures that no JMX or other metrics are created for Keyspace and ColumnFamilyStore objects that are opened without loading SSTables.

Some highlights (and possible reasons why this solution won't work):

• This uses the openSSTables flag to determine whether or not metrics are collected. The reasoning being that "If the SSTables are loaded, then we probably don't care about the metrics either". However, that may not be true! In that case, we may want to modify this to include a distinct "metrics" flag, or explicitly pass in a metrics factory, or similar.
• The trivial approach(replace KeyspaceMetrics with null) is a less disruptive change on the surface, but other code throughout the system appears to implicitly depend on the metrics object not being null. Enough of that existed throughout the codebase that the choice became "guarantee that every possible usage allows for null entries" or "risk a NPE if I am wrong about whether or not this case will always be used correctly". I opted for the slightly more disruptive approach of creating a subclass that doesn't register metrics. If you are a person with more knowledge of the C* codebase and has more confident that the nullity solution will work, then I'm open to being convinced. But this approach seemed to be safer overall.

[github-actions]

Checklist before you submit for review

• This PR adheres to the Definition of Done
• 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
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
82.2% Coverage on New Code
7.8% Duplication on New Code

See analysis details on SonarQube Cloud

[cassci-bot]

❌ Build ds-cassandra-pr-gate/PR-2272 rejected by Butler

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6 regressions found
See build details here

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Found 6 new test failures

Test	Explanation	Runs	Upstream
o.a.c.index.sai.cql.VectorCompaction100dTest.testOneToOneCompaction[version=ec enableNVQ=true]	REGRESSION	🔴⚪	0 / 30
o.a.c.index.sai.cql.VectorKeyRestrictedOnPartitionTest.partitionRestrictedTest[version=fa enableNVQ=true enableFused=false] (compression)	REGRESSION	🔴⚪	0 / 30
o.a.c.index.sai.cql.VectorSiftSmallTest.testCompaction[version=ed enableNVQ=true enableFused=false]	REGRESSION	🔴⚪	0 / 30
o.a.c.index.sai.cql.VectorUpdateDeleteTest.testTTLOverwriteHasCorrectOnDiskRowCount[version=eb enableNVQ=false enableFused=false] (compression)	REGRESSION	🔵🔴	0 / 30
o.a.c.metrics.KeyspaceMetricsTest.testMetricsNotRecordedWhenDisabled (compression)	NEW	🔴🔴	0 / 30
o.a.c.repair.RepairJobTest.testNoTreesRetainedAfterDifference (compression)	REGRESSION	🔴🔴	0 / 30

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Found 7 known test failures