feat: add webhooks (#334)

packages/sdk/index.ts

@@ -1,3 +1,17 @@
 export { UseSend } from "./src/usesend";
 export { UseSend as Unsend } from "./src/usesend"; // deprecated alias
 export { Campaigns } from "./src/campaign";
+export {
+  Webhooks,
+  WebhookVerificationError,
+  WEBHOOK_EVENT_HEADER,
+  WEBHOOK_CALL_HEADER,
+  WEBHOOK_SIGNATURE_HEADER,
+  WEBHOOK_TIMESTAMP_HEADER,
+} from "./src/webhooks";
+export type {
+  WebhookEvent,
+  WebhookEventData,
+  WebhookEventPayloadMap,
+  WebhookEventType,
+} from "./src/webhooks";