Add OCSF DNS Activity pipeline for DNSFilter (DataDog#23922)

* Add OCSF DNS Activity [4003] pipeline for DNSFilter

Map DNSFilter DNS query/filtering logs to OCSF DNS Activity class with
the security_control profile. Includes disposition, action, severity,
rcode, firewall_rule, and full endpoint mappings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Fix OCSF facet definitions to match canonical shared definitions

Update facet names, types, and facetType to match the definitions
used by other integrations as required by validate-logs CI check.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* expand rcode coverage

* hardcode activity_name

* tweak sev levels

* add targets

* align test output

* align test output

* Align test sample JSON formatting with CI pipeline output

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Align test result YAML formatting with CI pipeline output

Match CI's YAML serialization style: quoted strings, list indent.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: jbfeldman-dd