update admin proxies: handle ACME DNS 01 proxy

admin/assets/.well-known/telebit.app/index.json

@@ -3,7 +3,10 @@
     "api_host": ":hostname/api",
     "authn": {
         "method": "GET",
-        "pathname": "inspect"
+        "pathname": ""
+    },
+    "acme_dns_01_proxy": {
+        "pathname": "dns"
     },
     "pair_request": {
         "method": "POST",

cmd/telebit/admin.go

@@ -53,9 +53,15 @@ func InitAdmin(authURL string) {
 		r.URL.Path = strings.TrimPrefix(r.URL.Path, "/api")
 		proxyHandler.ServeHTTP(w, r)
 	}
+
+	// Proxy mgmt server Registration & Authentication
 	r.Get("/api/inspect", proxyHandleFunc)
+	r.Post("/api/register-device", proxyHandleFunc)
 	r.Post("/api/register-device/*", proxyHandleFunc)
 
+	// Proxy mgmt server ACME DNS 01 Challenges
+	r.Get("/api/dns/*", proxyHandleFunc)
+
 	r.Route("/api", func(r chi.Router) {
 		// TODO token needs a globally unique subject