Commands: Fix xray api adrules c1.json c2.json (#7276)

https://github.com/XTLS/Xray-core/pull/7276#pullrequestreview-5680949792

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Co-authored-by: 风扇滑翔翼 <Fangliding.fshxy@outlook.com>

main/commands/all/api/rules_add.go

@@ -92,6 +92,8 @@ func executeAddRules(cmd *base.Command, args []string) {
 		if err != nil {
 			base.Fatalf("failed to perform AddRule: %s", err)
 		}
+		// if multiple files are specified, use append to merge them instead of overriding previous one
+		shouldAppend = true
 		showJSONResponse(resp)
 	}
 }