Update config to reflect valid option

Signed-off-by: raffi-tamizian <raffi.tamizian@justeattakeaway.com>

.changeset/cold-seas-end.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-common': patch
+---
+
+Updates config.d.ts to reflect valid redis cache config option

packages/backend-common/config.d.ts

@@ -191,6 +191,11 @@ export interface Config {
           connection: string;
           /** An optional default TTL (in milliseconds). */
           defaultTtl?: number;
+          /**
+           * Whether or not [useRedisSets](https://github.com/jaredwray/keyv/tree/main/packages/redis#useredissets) should be configured to this redis cache.
+           * Defaults to true if unspecified.
+           */
+          useRedisSets?: boolean;
         }
       | {
           store: 'memcache';