tower: Use tx.set_request() to set HTTP request metadata

Without this the transaction does not have any HTTP request metadata attached, because apparently the event processor is not running for performance traces.

Note that I had to reorder the contents of the `configure_scope()` callback to be able to access `sentry_req` before it disappears into the `add_event_processor()` callback.

sentry-tower/src/http.rs

@@ -86,20 +86,21 @@ where
         let slf = self.project();
         if let Some((sentry_req, trx_ctx)) = slf.on_first_poll.take() {
             sentry_core::configure_scope(|scope| {
-                scope.add_event_processor(move |mut event| {
-                    if event.request.is_none() {
-                        event.request = Some(sentry_req.clone());
-                    }
-                    Some(event)
-                });
-
                 if let Some(trx_ctx) = trx_ctx {
                     let transaction: sentry_core::TransactionOrSpan =
                         sentry_core::start_transaction(trx_ctx).into();
+                    transaction.set_request(sentry_req.clone());
                     let parent_span = scope.get_span();
                     scope.set_span(Some(transaction.clone()));
                     *slf.transaction = Some((transaction, parent_span));
                 }
+
+                scope.add_event_processor(move |mut event| {
+                    if event.request.is_none() {
+                        event.request = Some(sentry_req);
+                    }
+                    Some(event)
+                });
             });
         }
         match slf.future.poll(cx) {