[Feature]: Support ResNeSt backbone (#2959)

* add stem_channels opt

* add ResNeSt

* fixed config

* fixed cascade config

* add precise BN

* add precise bn in test

* format precise bn

* update precise bn interval

* fixed eval config bug

* fixed precise interval

* change to return_loss=False

* add naive syncbn

* add naive syncbn

* rmo precise bn

* add range ms

* change to MMSyncBN

* add naive

* fixed loader

* reset test

* fixed faster config bug

* add no norm decay

* add baseline no norm decay

* set fronzen_stages=-1

* move import

* restore to official setting

* set to MMSyncBN

* update s101 pretrain

* update docs

* fixed config

* add backbone+head

* change fpn init

* add s101

* add s101

* revert fpn init

* add modelzoo, docstring, test

* fixed test

* fixed test

* add missing models

* update docstring

* add comment

* fixed markdownlint