make EventParams typed for tidier event handling

Signed-off-by: Brian Fletcher <brian@roadie.io>

.changeset/thick-tables-travel.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-events-node': patch
+---
+
+Make `EventParams` typed for implementing tidier event handling.

plugins/events-node/src/api/EventParams.ts

@@ -17,7 +17,7 @@
 /**
  * @public
  */
-export interface EventParams {
+export interface EventParams<PayloadType = unknown> {
   /**
    * Topic for which this event should be published.
    */
@@ -25,7 +25,7 @@ export interface EventParams {
   /**
    * Event payload.
    */
-  eventPayload: unknown;
+  eventPayload: PayloadType;
   /**
    * Metadata (e.g., HTTP headers and similar for events received from external).
    */