feat(alerting): add support for uploading images to webdav.

closes #5770

pkg/setting/setting.go

@@ -153,6 +153,8 @@ var (
 	S3TempImageStoreBucketUrl string
 	S3TempImageStoreAccessKey string
 	S3TempImageStoreSecretKey string
+
+	ImageUploadProvider string
 )
 
 type CommandLineArgs struct {
@@ -539,10 +541,8 @@ func NewConfigContext(args *CommandLineArgs) error {
 
 	GrafanaNetUrl = Cfg.Section("grafana.net").Key("url").MustString("https://grafana.net")
 
-	s3temp := Cfg.Section("s3-temp-image-store")
-	S3TempImageStoreBucketUrl = s3temp.Key("bucket_url").String()
-	S3TempImageStoreAccessKey = s3temp.Key("access_key").String()
-	S3TempImageStoreSecretKey = s3temp.Key("secret_key").String()
+	imageUploadingSection := Cfg.Section("external_image_storage")
+	ImageUploadProvider = imageUploadingSection.Key("provider").MustString("internal")
 	return nil
 }