Feat: improve thumbnails proformance and GC for local policy (#1044)

* thumb generating improvement

Replace "github.com/nfnt/resize" with "golang.org/x/image/draw". Add thumb task queue to avoid oom when batch thumb operation

* thumb improvement

* Add some tests for thumbnail generation

pkg/conf/conf.go

@@ -70,9 +70,13 @@ type redis struct {
 
 // 缩略图 配置
 type thumb struct {
-	MaxWidth   uint
-	MaxHeight  uint
-	FileSuffix string `validate:"min=1"`
+	MaxWidth      uint
+	MaxHeight     uint
+	FileSuffix    string `validate:"min=1"`
+	MaxTaskCount  int
+	EncodeMethod  string `validate:"eq=jpg|eq=png"`
+	EncodeQuality int    `validate:"gte=1,lte=100"`
+	GCAfterGen    bool
 }
 
 // 跨域配置