Fix the bug that MAISI ckpt cannot be loaded after finetune.

[guopengf]

Fixes # .

Description

MAISI output checkpoint after finetuning cannot be used as trained_controlnet_path.
This problem came from the CheckpointSaver. When a single key is provided for save_dict such as:
"save_dict": {
"controlnet_state_dict": "@ControlNet"
},
The saved dict does contain the key " "controlnet_state_dict". However, it directly saves the state_dict of controlnet as the checkpoint.

The workaround is that we also save the optimizer state. For example,
"save_dict": {
"controlnet_state_dict": "@ControlNet",
"optimizer": "@optimizer"
}. Then, the MAISI output checkpoint after fine-tuning can be properly loaded.

Status

Ready/Work in progress/Hold

Please ensure all the checkboxes:

• Codeformat tests passed locally by running ./runtests.sh --codeformat.
• In-line docstrings updated.
• Update version and changelog in metadata.json if changing an existing bundle.
• Please ensure the naming rules in config files meet our requirements (please refer to: CONTRIBUTING.md).
• Ensure versions of packages such as monai, pytorch and numpy are correct in metadata.json.
• Descriptions should be consistent with the content, such as eval_metrics of the provided weights and TorchScript modules.
• Files larger than 25MB are excluded and replaced by providing download links in large_file.yml.
• Avoid using path that contains personal information within config files (such as use /home/your_name/ for "bundle_root").

[KumoLiu]

Thanks for the fix, looks good to me.

[KumoLiu]

/build