clean up useless binlog files

[jd-zhang]

*Issue migrated from trac ticket # 734 www.kunlunbase.com *

component: node manager | priority: major

2022-05-25 15:15:47: zhaowei@zettadb.com created the issue

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delete a node's binlog files if

1. such binlog files are already stream backed up
2. all of the node's replicas if any have retrieved the binlog files.
   consider report IO thread progress(latest retrieved master binlog pos&gtid) to metadata shard.
3. keep most recent 7 binlog files

[jd-zhang]

2022-05-30 10:52:56: zhaowei@zettadb.com edited the issue description