enh(query): add distributed splitting of aggregate function 

feat: support multi-way sort merge

fix:return false in is ture operator if result is null

Merge branch 'szhou/feature/multiwaymerge' of github.com:taosdata/TDengine into szhou/feature/multiwaymerge

feat: physical plan add clone interface

feat(stream): distributed stream interval

refactor(stream)

enh(stream): direct sink if not dispatch

fix:return false in is ture operator if result is null