style: extend --brief row-filter to other plugins with unbounded table output

[markuslf]

Context

#782 (disk-usage) and #788 (dhcp-scope-usage) introduced --brief, the row-level counterpart of the column-level --lengthy switch. --brief hides table rows within the thresholds so only items in WARN/CRIT state are shown. The semantics are documented in CONTRIBUTING under "Verbosity parameter convention": orthogonal to --lengthy, not mutually exclusive, perfdata and alerting are unaffected.

Several other plugins emit tables that can grow unbounded on large deployments. On such systems, the default output is often longer than the event-console output limit, and the admin has no way to see just the interesting rows without piping the check through grep. These plugins would benefit from the same --brief treatment.

Non-goals

• Do not add --brief to plugins whose default output is already a single line (e.g. cpu-usage, load, uptime). --brief only makes sense where the default output is a table or an itemized list.
• Do not change the alerting logic or the perfdata emission. --brief is strictly a display filter per the convention in CONTRIBUTING.
• Do not make --brief and --lengthy mutually exclusive.

Reference implementations

• check-plugins/disk-usage and check-plugins/dhcp-scope-usage.
• CONTRIBUTING section "Verbosity parameter convention" documents the rules.

Classification

Enhancement. Non-breaking (additive parameter, default off).