[v10.0.x] Plugins: Only configure plugin proxy transport once (#71742)

Plugins: Only configure plugin proxy transport once (#71735)

only configure plugin proxy transport once

(cherry picked from commit b59ca7fb22)

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

pkg/api/plugin_proxy.go

@@ -14,9 +14,12 @@ import (
 	"github.com/grafana/grafana/pkg/web"
 )
 
+var (
+	once                 sync.Once
+	pluginProxyTransport *http.Transport
+)
+
 func (hs *HTTPServer) ProxyPluginRequest(c *contextmodel.ReqContext) {
-	var once sync.Once
-	var pluginProxyTransport *http.Transport
 	once.Do(func() {
 		pluginProxyTransport = &http.Transport{
 			TLSClientConfig: &tls.Config{