[ckpt] feat: integrate checkpoint resume in RL ray trainer

[PeterSH6]

Features:

• Save actor and critic checkpoint:
  • Model
  • Optimizer
  • lr_scheduler
  • rng_state
  • dataloader
• A complete checkpoint represents that dataloader, actor and critic (if any) state are properly saved
• By default, we will not save the dataset but only store the dataloader (with sampler) state

Usage:

• Support resume mode: auto, disable and resume_from_path
  • auto: veRL will automatically check the latest checkpoint from trainer.default_local_dir
  • disable: veRL will always train from scratch
  • resume_from_path: When setting resume_from_path=True, then user only need to set the resume_mode to the checkpoint path that you want to load.

TODO:

• Support SFT resume in the next PR
• Support uploader

Relevant issue:

• Resume from checkpoints #76
• Does verl support Breakpoint retraining ？ #143