Add disk caching for youtube api calls

Fixes https://github.com/ajayyy/SponsorBlockServer/issues/239

src/utils/diskCache.ts

@@ -0,0 +1,32 @@
+import LRU from "@ajayyy/lru-diskcache";
+import { config } from "../config";
+
+let DiskCache: LRU<string, string>;
+
+if (config.diskCache) {
+    DiskCache = new LRU('./databases/cache', config.diskCache);
+    DiskCache.init();
+} else {
+    DiskCache = {
+        // constructor(rootPath, options): {};
+
+        init() {},
+
+        reset() {},
+
+        has(key) { return false; },
+
+        get(key, opts) { return null; },
+
+        // Returns size
+        set(key, dataOrSteam) { return new Promise((resolve) => 0); },
+
+        del(key) {},
+
+        size() { return 0; },
+
+        prune() {},
+    };
+}
+
+export default DiskCache;