Use zstd instead of gzip if available

Add zstd to cache versioning

src/constants.ts

@@ -19,7 +19,15 @@ export enum Events {
     PullRequest = "pull_request"
 }
 
-export const CacheFilename = "cache.tgz";
+export enum CacheFilename {
+    Gzip = "cache.tgz",
+    Zstd = "cache.tzst"
+}
+
+export enum CompressionMethod {
+    Gzip = "gzip",
+    Zstd = "zstd"
+}
 
 // Socket timeout in milliseconds during download.  If no traffic is received
 // over the socket during this period, the socket is destroyed and the download