exec replica::garbage_collection() in background thread
exec replica::garbage_collection() in background thread

Summary: Ref T9259

Test Plan: N/A

Reviewers: sunweijie, shenyuannan, cailiuyang

Reviewed By: sunweijie

Subscribers: #pegasus

Maniphest Tasks: T9259

Differential Revision: https://phabricator.d.xiaomi.net/D62864

shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN