added backup apis and tests

models/backup_file_info.go

@@ -0,0 +1,9 @@
+package models
+
+import "github.com/pocketbase/pocketbase/tools/types"
+
+type BackupFileInfo struct {
+	Key      string         `json:"key"`
+	Size     int64          `json:"size"`
+	Modified types.DateTime `json:"modified"`
+}