Sticky routing: record successes on update-gateway-score

[prajjwalkumar17]

Part of #393 (sticky routing). Status: implemented in #420 (commit 23f953b), pending review/merge.

POST /update-gateway-score gains three optional, backward-compatible fields:

{ "customerId": "cust_123", "paymentMethod": "INTERAC", "paymentMethodType": "RTP", ... }

• Payload wins; the decide-time gateway_scoring_data_{payment_id} snapshot (which now also stashes customerId) is the fallback — so callers only need the fields when success webhooks can outlive the snapshot's 30-minute TTL.
• Two-pass hook in check_and_update_gateway_score_: a payload-only pass runs before the snapshot fetch (a CHARGED webhook hours late still counts), the snapshot pass after.
• Writes only on CHARGED / AUTHORIZED / PARTIAL_CHARGED — the engine's wider success set includes lifecycle statuses (VOIDED, AUTO_REFUNDED, CAPTURE_FAILED, …) that would let a late webhook re-count an earlier attempt's connector. Retries are correct by construction: fail-on-A writes nothing, success-on-B increments B.
• No dedupe, by design: update-gateway-score is the source of truth — every event counts, N times if sent N times (matching the engine default SR behavior; its feedback locks are opt-in per merchant).
• Bug fixed en route: the GSM healthy-failure early-return now fires on failures only — previously a success carrying errorInfo skipped both the SR reward and any snapshot-based work.
• Gated by the sticky_routing_enabled FeatureConf; a sticky write failure is logged, never surfaced to the caller. openapi + api-refs updated.