Replace usage of http.DefaultClient and http.DefaultTransport (#104135)

Remove usage of http.DefaultClient and http.DefaultTransport

Part of grafana/data-sources#484

pkg/tsdb/cloudwatch/cloudwatch.go

@@ -3,7 +3,6 @@ package cloudwatch
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
 	"time"
@@ -324,14 +323,7 @@ func (ds *DataSource) newSession(region string) (*session.Session, error) {
 		// only update the transport to try to avoid the issue mentioned here https://github.com/grafana/grafana/issues/46365
 		// also, 'sess' is cached and reused, so the first time it might have the transport not set, the following uses it will
 		if sess.Config.HTTPClient.Transport == nil {
-			// following go standard library logic (https://pkg.go.dev/net/http#Client), if no Transport is provided,
-			// then we use http.DefaultTransport
-			defTransport, ok := http.DefaultTransport.(*http.Transport)
-			if !ok {
-				// this should not happen but validating just in case
-				return nil, errors.New("default http client transport is not of type http.Transport")
-			}
-			sess.Config.HTTPClient.Transport = defTransport.Clone()
+			sess.Config.HTTPClient.Transport = httpclient.NewHTTPTransport()
 		}
 		err = proxy.New(ds.ProxyOpts).ConfigureSecureSocksHTTPProxy(sess.Config.HTTPClient.Transport.(*http.Transport))
 		if err != nil {