feat(personhog): add caller tag to property-defs-rs

[nickbest-ph]

Problem

We need per-caller attribution on personhog gRPC requests to identify which code paths are generating heavy traffic. The x-caller-tag header (consumed by the router in PR #60361) provides this, but each client service needs to send it.

Changes

Adds x-caller-tag: property-defs/group-type-resolution metadata header to the gRPC request in the property-defs-rs group type resolver. This is a single-line addition alongside the existing x-client-name header.

Deploy target: property-defs-rs

Note: The router (PR #60361) must deploy first to consume this header. Until then, the header is harmlessly ignored.

How did you test this code?

• Verified clippy passes with no warnings
• The change is a trivial metadata insertion following the exact same pattern as the existing x-client-name header on the adjacent line

Publish to changelog?

No

Docs update

N/A

🤖 Agent context

Cherry-picked from nick/personhog-query-tagging development branch. Part of a 4-PR series adding x-caller-tag attribution across the personhog stack:

1. PR feat(personhog): extract x-caller-tag header in router #60361 — Router extraction (Rust) — must deploy first
2. This PR — property-defs-rs static tag
3. Node.js client caller tag
4. Django interceptor + middleware + manual tags

[greptile-apps]

_{Reviews (1): Last reviewed commit: "feat(personhog): add caller tag to prope..." | Re-trigger Greptile}

[deployment-status-posthog]

Deploy status

Environment	Status	Deployed At	Workflow
dev	✅ Deployed	2026-05-27 23:50 UTC	Run
prod-us	✅ Deployed	2026-05-28 00:02 UTC	Run
prod-eu	✅ Deployed	2026-05-28 00:04 UTC	Run