httpserver: Add nicolasazrak/caddy-cache plugin directive (#1759)

caddyhttp/httpserver/plugin.go

@@ -453,6 +453,7 @@ var directives = []string{
 	// directives that add middleware to the stack
 	"locale", // github.com/simia-tech/caddy-locale
 	"log",
+	"cache", // github.com/nicolasazrak/caddy-cache
 	"rewrite",
 	"ext",
 	"gzip",