[exporter/datadog] Avoid logging in chain provider goroutines to avoi…

…d data race (open-telemetry#24899)

**Description:** 

Fixes data race on `TestChain` that was caused by logging after the test
was ended (see
uber-go/zap#687 (comment) for
details).
To do this, we move the logging outside of the goroutines in the Chain
provider.
Goroutines can still be running after the function has returned (this is
intentional, their return value will just be ignored), but they will no
longer log anything.

I also made the `Source` method honor cancellation of the context when
waiting on providers.

**Link to tracking Issue:** Reported on Slack, see
https://cloud-native.slack.com/archives/C01N6P7KR6W/p1691074033049049?thread_ts=1690992010.123699&cid=C01N6P7KR6W

exporter/datadogexporter/internal/hostmetadata/provider/provider.go

@@ -37,32 +37,28 @@ func (p *chainProvider) Source(ctx context.Context) (source.Source, error) {
 	for i, source := range p.priorityList {
 		provider := p.providers[source]
 		replies[i] = make(chan reply)
-
-		go func(i int, source string) {
-			zapProvider := zap.String("provider", source)
-			p.logger.Debug("Trying out source provider", zapProvider)
-
+		p.logger.Debug("Trying out source provider", zap.String("provider", source))
+		go func(i int) {
 			src, err := provider.Source(ctx)
-			if err != nil {
-				p.logger.Debug("Unavailable source provider", zapProvider, zap.Error(err))
-			}
-
 			replies[i] <- reply{src: src, err: err}
-		}(i, source)
+		}(i)
 	}
 
 	// Check provider responses in order to ensure priority
 	for i, ch := range replies {
-		reply := <-ch
-		if reply.err != nil {
-			// Provider was unavailable, error was logged on goroutine
-			continue
-		}
+		zapProvider := zap.String("provider", p.priorityList[i])
+		select {
+		case <-ctx.Done():
+			return source.Source{}, fmt.Errorf("context was cancelled: %w", ctx.Err())
+		case reply := <-ch:
+			if reply.err != nil {
+				p.logger.Debug("Unavailable source provider", zapProvider, zap.Error(reply.err))
+				continue
+			}
 
-		p.logger.Info("Resolved source",
-			zap.String("provider", p.priorityList[i]), zap.Any("source", reply.src),
-		)
-		return reply.src, nil
+			p.logger.Info("Resolved source", zapProvider, zap.Any("source", reply.src))
+			return reply.src, nil
+		}
 	}
 
 	return source.Source{}, fmt.Errorf("no source provider was available")