feat: new options for finegrained control of caching

* `CACHE_REDIRECT`: controls server caching of redirects
* `CACHE_CLIENT_REDIRECT`: controls client caching of redirects
* `REDIRECT_FASTPATH`: controls if redirects should be resolved
  to the contents of the Location URL (if already cached)

.env.defaults

@@ -1,7 +1,9 @@
 UPSTREAM_ORIGIN=https://esm.sh
 BASE_PATH=/
 CACHE=false
+CACHE_REDIRECT=600
 CACHE_CLIENT_REDIRECT=600
 HOMEPAGE=https://github.com/esroyo/systemjs.sh
 OUTPUT_BANNER=/* systemjs.sh */
+REDIRECT_FASTPATH=true
 WORKER_ENABLE=false

.env.example

@@ -1,6 +1,8 @@
 UPSTREAM_ORIGIN=https://esm.sh
 BASE_PATH=/
 CACHE=true
+CACHE_REDIRECT=600
 CACHE_CLIENT_REDIRECT=600
 HOMEPAGE=https://github.com/esroyo/systemjs.sh
+REDIRECT_FASTPATH=true
 OUTPUT_BANNER=/* Systemjs output */