br: update restore checkpoint information

[Leavrth]

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  br: migrate pitr id map to the system table mysql.tidb_pitr_id_map tidb#55871

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[3pointer]

Suggested change

	在第一次执行恢复时，br 工具会首先进入快照恢复阶段，这与上述只进行快照恢复操作相同。当 br 工具进入到快照恢复阶段，备份数据的上游集群的 ID 和备份数据的 BackupTS （等于日志恢复的起始时间点 `start-ts`）已经被记录于断点中。这意味着当恢复在快照恢复阶段执行失败时，尝试断点恢复继续时无法再调整快照备份路径（等于日志恢复的启示时间点 `restored-ts`）.
	在第一次执行恢复时，br 工具会首先进入快照恢复阶段，这与上述只进行快照恢复操作相同。当 br 工具进入到快照恢复阶段，备份数据的上游集群的 ID 和备份数据的 BackupTS （等于日志恢复的起始时间点 `start-ts`）已经被记录于断点中。这意味着当恢复在快照恢复阶段执行失败时，尝试断点恢复继续时无法再调整快照备份路径（等于日志恢复的起始时间点 `restored-ts`）.

[3pointer]

🤔这句话有点绕