Bug 2064758 - Only log remote settings downloads on error (#7592)

We got reports that there were generating lots of log lines on iOS
(breadcrumbs are also logged as warnings to the console).  I changed the
code to only report the breadcrumbs for error downloads, which should
allow us to track down bad URLs without overloading the log files.

Another option was to only report the breadcrumb, but not log.  I didn't
like this one, since I think the same issue could spam the
breadcrumb list and make them less useful.

Author: bendk

components/remote_settings/src/client.rs

@@ -647,7 +647,11 @@ impl ViaductApiClient {
     }
 
     fn make_request(&mut self, url: Url) -> Result<Response> {
-        breadcrumb!("make_request: {url}");
+        self._make_request(url.clone())
+            .inspect_err(|e| breadcrumb!("Request error: {e} ({url})"))
+    }
+
+    fn _make_request(&mut self, url: Url) -> Result<Response> {
         self.remote_state.ensure_no_backoff()?;
 
         let req = Request::get(url);