appender: name spawned thread (#2219)

## Motivation

I find it useful when debugging applications with lots of threads to
easily identity them by their names.

## Solution

Just name the thread as other crates such as `sentry-rust` are doing.

Co-authored-by: Guillaume Desmottes <guillaume@desmottes.be>

Author: gdesmott

tracing-appender/src/worker.rs

@@ -68,22 +68,25 @@ impl<T: Write + Send + Sync + 'static> Worker<T> {
 
     /// Creates a worker thread that processes a channel until it's disconnected
     pub(crate) fn worker_thread(mut self) -> std::thread::JoinHandle<()> {
-        thread::spawn(move || {
-            loop {
-                match self.work() {
-                    Ok(WorkerState::Continue) | Ok(WorkerState::Empty) => {}
-                    Ok(WorkerState::Shutdown) | Ok(WorkerState::Disconnected) => {
-                        let _ = self.shutdown.recv();
-                        break;
-                    }
-                    Err(_) => {
-                        // TODO: Expose a metric for IO Errors, or print to stderr
+        thread::Builder::new()
+            .name("tracing-appender".to_string())
+            .spawn(move || {
+                loop {
+                    match self.work() {
+                        Ok(WorkerState::Continue) | Ok(WorkerState::Empty) => {}
+                        Ok(WorkerState::Shutdown) | Ok(WorkerState::Disconnected) => {
+                            let _ = self.shutdown.recv();
+                            break;
+                        }
+                        Err(_) => {
+                            // TODO: Expose a metric for IO Errors, or print to stderr
+                        }
                     }
                 }
-            }
-            if let Err(e) = self.writer.flush() {
-                eprintln!("Failed to flush. Error: {}", e);
-            }
-        })
+                if let Err(e) = self.writer.flush() {
+                    eprintln!("Failed to flush. Error: {}", e);
+                }
+            })
+            .expect("failed to spawn `tracing-appender` non-blocking worker thread")
     }
 }