feat(spooler): Add back metrics

relay-server/src/services/buffer/envelope_buffer/mod.rs

@@ -86,6 +86,7 @@ impl EnvelopeBuffer {
 
     /// Pushes an envelope to the [`EnvelopeRepository`] and updates the priority queue accordingly.
     pub async fn push(&mut self, envelope: Box<Envelope>) -> Result<(), EnvelopeBufferError> {
+        relay_statsd::metric!(counter(RelayCounters::BufferEnvelopesWritten) += 1);
         relay_statsd::metric!(timer(RelayTimers::BufferPush), {
             let received_at = envelope.meta().start_time().into();
             let project_key_pair = ProjectKeyPair::from_envelope(&envelope);
@@ -136,6 +137,7 @@ impl EnvelopeBuffer {
     /// The priority of the [`ProjectKeyPair`] is updated with the next envelope's received_at
     /// time.
     pub async fn pop(&mut self) -> Result<Option<Box<Envelope>>, EnvelopeBufferError> {
+        relay_statsd::metric!(counter(RelayCounters::BufferEnvelopesRead) += 1);
         relay_statsd::metric!(timer(RelayTimers::BufferPop), {
             let Some((&project_key_pair, _)) = self.priority_queue.peek() else {
                 return Ok(None);