webhook: add pluggable Store interface to RouteLogger

[dksogal]

Summary

RouteLogger currently only knows about keys registered in its own process's in-memory map. During a rolling deploy of a consumer (e.g. mme-e2e), a webhook callback can arrive at a different process/pod than the one that registered the test, and is silently dropped by Record.

This adds an additive Store interface (Publish / Unpublish / Forward) that RouteLogger.Sent / Record / Delete consult, so a caller can plug in cross-process delivery (e.g. a shared cache keyed by pod) without Orbital taking on any new dependency.

• Default behavior (localStore, used when no Store is configured) is identical to current behaviour.
• NewRouteLogger's existing signature is unchanged — the new opts ...RouteLoggerOption param is backward compatible, so no existing caller needs to change.
• Wait / WaitN are untouched — the reflect.Select multi-key wait stays exactly as-is.

Test plan

• /review-toolkit:review has been run
• go build ./... and go test ./webhook/... -race -v pass, including the two pre-existing tests unmodified.
• New tests (store_test.go) use a bare bookkeeping registry double (no decision logic of its own) so the assertions exercise real RouteLogger wiring:
  • TestRouteLoggerStoreForwardsCrossPodDelivery — a callback that misses locally on one RouteLogger instance is delivered to a second instance via Store.Forward, unblocking its Wait.
  • TestRouteLoggerStoreNotCalledOnLocalHit — a local hit never calls Forward.
  • TestRouteLoggerDeleteUnpublishesFromStore — Delete releases ownership in the store, not just locally.
  • Verified these tests are load-bearing by mutating the implementation locally (removing the Forward-on-miss call, and making Record forward unconditionally) and confirming each mutation was caught.
• Confirmed mme-e2e's two existing webhook.NewRouteLogger(...) call sites compile unmodified against this branch via a local replace directive.

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