docs(zabbix): add Trigger on-call pages section

[Kyle-Neale]

Summary

Adds a "Trigger on-call pages" section to zabbix/README.md documenting how to forward Zabbix triggers to Datadog On-Call using the oncall_team query parameter on the V2 events webhook intake.

Implementation uses a JavaScript Webhook media type (Zabbix's native notification surface, parallel to the existing legacy Datadog media type already documented in the same README). The script builds the V2 envelope client-side, so no VRL transformer is required.

Notes for reviewers

• Payload matches the canonical V2 webhook intake schema from the start (per DataDog/dd-source nagios/success_basecase.json): JSON:API envelope (data.type + data.attributes), integration_id: "zabbix", nested attributes.status (warn/error/ok), and a zabbix.source namespaced object — analogous to nagios.source in the canonical example.
• Severity mapping: PROBLEM + High/Disaster → error; PROBLEM + Warning/Average/Information/Not-classified → warn (no silent drops); OK → ok (resolves the page via shared aggregation_key).
• Companion to integrations-core#22991 (Nagios), same feature family from the EvMgt On-Call swap-and-go RFC.

Tracks BGL-1967.

Test plan

• Render preview of the new section on GitHub
• Manual end-to-end: create the media type with the script, fire a test trigger, verify a page lands under On-Call > Pages, fire a recovery, verify auto-resolve

🤖 Generated with Claude Code

[Kyle-Neale]

Open question for reviewers: the V2 webhook intake VRL (zabbix.vrl) sanitizes oversized fields — aggregation_key is MD5'd above 100 chars, title is truncated to 500, message to 4000, tags to 100 items × 200 chars each.

Worth adding a short "Payload limits" note to this section, or is the sanitizer's fail-open behavior fine to leave undocumented?

[jeff-morgan-dd]

Created DOCS-14513 for editorial review.

[warthy]

Open question for reviewers: the V2 webhook intake VRL (zabbix.vrl) sanitizes oversized fields — aggregation_key is MD5'd above 100 chars, title is truncated to 500, message to 4000, tags to 100 items × 200 chars each.

Worth adding a short "Payload limits" note to this section, or is the sanitizer's fail-open behavior fine to leave undocumented?

@Kyle-Neale As those limits might vary I don't think it's worth documenting for now