Put source error into the Display impl of Status

Here's how the error looks before this change:

```
status: 'Some resource has been exhausted', self: "h2 protocol error: http2 error"
```

And here it is after:

```
status: 'Some resource has been exhausted', self: "h2 protocol error: http2 error", source: tonic::transport::Error(Transport, hyper::Error(Http2, Error { kind: GoAway(b"ivan_says_hello", ENHANCE_YOUR_CALM, Remote) }))
```

The latter gives the user a lot more context about the issue.

Author: bobrik

tonic/src/status.rs

@@ -757,6 +757,9 @@ impl fmt::Display for Status {
         if !self.metadata().is_empty() {
             write!(f, ", metadata: {:?}", self.metadata().as_ref())?;
         }
+        if let Some(source) = self.source() {
+            write!(f, ", source: {source:?}")?;
+        }
         Ok(())
     }
 }