Use clone of http.DefaultTransport (#449)

Instead of using the DefaultTransport directly clone it and make sure it
is what we expect.

Author: itsmylife

.changeset/smooth-otters-enjoy.md

@@ -0,0 +1,5 @@
+---
+'grafana-github-datasource': patch
+---
+
+Get default http transport from plugin-sdk-go

cspell.config.json

@@ -22,6 +22,7 @@
     "grafanabot",
     "groupby",
     "healthcheck",
+    "httpclient",
     "HTMLURL",
     "instancemgmt",
     "jackspeak",

pkg/github/client/client.go

@@ -11,11 +11,13 @@ import (
 
 	"github.com/bradleyfalzon/ghinstallation/v2"
 	googlegithub "github.com/google/go-github/v53/github"
-	"github.com/grafana/github-datasource/pkg/models"
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/grafana/grafana-plugin-sdk-go/backend/httpclient"
 	"github.com/influxdata/tdigest"
 	"github.com/shurcooL/githubv4"
 	"golang.org/x/oauth2"
+
+	"github.com/grafana/github-datasource/pkg/models"
 )
 
 // Client is a wrapper of GitHub clients that can access the GraphQL and rest API.
@@ -74,7 +76,11 @@ func createAppClient(settings models.Settings) (*Client, error) {
 		return nil, backend.DownstreamError(errors.New("error parsing installation id"))
 	}
 
-	itr, err := ghinstallation.New(http.DefaultTransport, appId, installationId, []byte(settings.PrivateKey))
+	transport, err := httpclient.GetDefaultTransport()
+	if err != nil {
+		return nil, backend.DownstreamError(errors.New("error: http.DefaultTransport is not of type *http.Transport"))
+	}
+	itr, err := ghinstallation.New(transport, appId, installationId, []byte(settings.PrivateKey))
 	if err != nil {
 		return nil, backend.DownstreamError(errors.New("error creating token source"))
 	}