add cache behavior modifiers to RequestInit interface

documentation for these features can be found at https://developers.cloudflare.com/workers/about/using-cache/

Author: trjstewart

index.d.ts

@@ -5,6 +5,8 @@ interface FetchEvent {
 interface RequestInit {
   cf?: {
     cacheEverything?: boolean
+    cacheTtl?: number
+    cacheTtlByStatus?: { [key: string]: number }
     scrapeShield?: boolean
     apps?: boolean
     image?: {