revert: drop POST /secret write support (back to read-only)

cmd/api/main.go

@@ -122,7 +122,6 @@ func main() {
 	api.Use(auth.Middleware(auth.NewStore(cfg.APIKeys)))
 
 	api.Get("/secret/:name", h.GetSecret)
-	api.Post("/secret", h.CreateSecret)
 	api.Post("/refresh", h.RefreshCache)
 
 	// Graceful shutdown.