Trajepl/nebula ckpt engine (#2085)
* enable checkpoint engine
* seprated nebula config
* add __init__.py for nebula importing
* linter fix
* fix: ds_config is None
* fix: ds config
* fix: get sd loader fix
* align the API with torch raw code
* linter fix
* remove duplicate tag params
* make checkpoint_engine as required args
* fix args
* extract parameters out to config
* fix: load state dict
* separate load engine
* linter fix
* extract checkpoint engine to abstract calss
* linter fix
* construct function args fix
* add docs for dev/customers
* linter fix
* remove load engine
* print->log_dist
* linter fix
* add tag flag to distinguish the loading order
Co-authored-by: Olatunji Ruwase <olruwase@microsoft.com>
Co-authored-by: Michael Wyatt <michaelwyatt@microsoft.com>
Co-authored-by: Jeff Rasley <jerasley@microsoft.com>
