feat(report) : Differences between vulnerability patched items (#1157)

* add plusDiff() and minusDiff()
* add plusDiff minusDiff test

Co-authored-by: Kota Kanbe <kotakanbe@gmail.com>

config/config.go

@@ -83,6 +83,8 @@ type Config struct {
 	FormatFullText    bool `json:"formatFullText,omitempty"`
 	FormatCsvList     bool `json:"formatCsvList,omitempty"`
 	GZIP              bool `json:"gzip,omitempty"`
+	DiffPlus          bool `json:"diffPlus,omitempty"`
+	DiffMinus         bool `json:"diffMinus,omitempty"`
 	Diff              bool `json:"diff,omitempty"`
 }