Plugins Proxy: Allow using {{ .URL }} inside "routes" section in plugin.json (#80858)

Signed-off-by: Slach <bloodjazman@gmail.com>
Co-authored-by: Andres Martinez Gotor <andres.mgotor@gmail.com>

pkg/api/pluginproxy/ds_auth_provider.go

@@ -16,6 +16,7 @@ import (
 type DSInfo struct {
 	ID                      int64
 	Updated                 time.Time
+	URL                     string
 	JSONData                map[string]any
 	DecryptedSecureJSONData map[string]string
 }
@@ -24,8 +25,8 @@ type DSInfo struct {
 func ApplyRoute(ctx context.Context, req *http.Request, proxyPath string, route *plugins.Route,
 	ds DSInfo, cfg *setting.Cfg) {
 	proxyPath = strings.TrimPrefix(proxyPath, route.Path)
-
 	data := templateData{
+		URL:            ds.URL,
 		JsonData:       ds.JSONData,
 		SecureJsonData: ds.DecryptedSecureJSONData,
 	}