CNDB-12240: Allow custom internode outbound metrics

[driftx]

What is the issue

These metrics needs to be customizable.

What does this PR fix and why was it fixed

Allow custom implementations.

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

[jkni]

LGTM. Are you also planning to expose InboundConnections' metrics? It seems straightforward enough to do here all at once.

[driftx]

Realized I need further changes here that will be more outbound-specific, so I'll update with those when ready.

[sonarqubecloud]

Quality Gate failed

Failed conditions
27.3% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud

[cassci-bot]

❌ Build ds-cassandra-pr-gate/PR-1470 rejected by Butler

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1 new test failure(s) in 4 builds
See build details here

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Found 1 new test failures

Test	Explanation	Branch history	Upstream history
...adRepairGuarantees.test_atomic_writes[blocking]	regression	🔴🔴🔴🔴	🔵🔵🔵🔵🔵🔵🔵

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Found 431 known test failures