fix(grpc): Allow gRPC connections via Unix socket

This commit addresses issue open-telemetry#1832.

The way `NET_PEER_IP` and `NET_PEER_PORT` are retrieved raises a `ValueError`
when gRPC connections are handled via Unix sockets.

```py
ip, port = (
    context.peer().split(",")[0].split(":", 1)[1].rsplit(":", 1)
)
```

When using an address like `unix:///tmp/grpc.sock` the value of `context.peer()` is `"unix:"`.
Substituting that in the function above...

```py
ip, port = "unix:".split(",")[0].split(":", 1)[1].rsplit(":", 1)
ip, port = ["unix:"][0].split(":", 1)[1].rsplit(":", 1)
ip, port = "unix:".split(":", 1)[1].rsplit(":", 1)
ip, port = ["unix", ""][1].rsplit(":", 1)
ip, port = "".rsplit(":", 1)
ip, port = [""]  # ValueError
```

I "addressed" the issue by guarding the retrieval of `net.peer.*` values under
an `if` statement that checks if we are using a Unix socket.

I extended the `server_interceptor` tests to run against TCP and Unix socket configurations.

---

**Open Questions**

- [ ] The socket tests will fail on Windows. Is there a way to annotate that?
- [ ] Are there other span values we should be setting for the unix socket?

Author: mattoberle

instrumentation/opentelemetry-instrumentation-grpc/src/opentelemetry/instrumentation/grpc/_server.py

@@ -250,24 +250,30 @@ def _start_span(
         # * ipv4:127.0.0.1:57284
         # * ipv4:10.2.1.1:57284,127.0.0.1:57284
         #
-        try:
-            ip, port = (
-                context.peer().split(",")[0].split(":", 1)[1].rsplit(":", 1)
-            )
-            ip = unquote(ip)
-            attributes.update(
-                {
-                    SpanAttributes.NET_PEER_IP: ip,
-                    SpanAttributes.NET_PEER_PORT: port,
-                }
-            )
+        if context.peer() != "unix:":
+            try:
+                ip, port = (
+                    context.peer()
+                    .split(",")[0]
+                    .split(":", 1)[1]
+                    .rsplit(":", 1)
+                )
+                ip = unquote(ip)
+                attributes.update(
+                    {
+                        SpanAttributes.NET_PEER_IP: ip,
+                        SpanAttributes.NET_PEER_PORT: port,
+                    }
+                )
 
-            # other telemetry sources add this, so we will too
-            if ip in ("[::1]", "127.0.0.1"):
-                attributes[SpanAttributes.NET_PEER_NAME] = "localhost"
+                # other telemetry sources add this, so we will too
+                if ip in ("[::1]", "127.0.0.1"):
+                    attributes[SpanAttributes.NET_PEER_NAME] = "localhost"
 
-        except IndexError:
-            logger.warning("Failed to parse peer address '%s'", context.peer())
+            except IndexError:
+                logger.warning(
+                    "Failed to parse peer address '%s'", context.peer()
+                )
 
         return self._tracer.start_as_current_span(
             name=handler_call_details.method,