Add vulnerability scanning scenario to test-on-cng pipeline

What does this MR do and why?

• Add configuration for Test::Integration::ContinuousVulnerabilityScanning scenario to test-on-cng/main.gitlab-ci.yml
• Remove this suite from e2e:test-on-omnibus to avoid duplicate executions
• Update docs with this addition
• Increase wait time in CVS spec to ensure test reliability

References

Related to gitlab-org/quality/quality-engineering/team-tasks#3987 (closed)

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