Allow Import Paths of Arbitrary Length

[fabianlim]

The import_module would be called only on a single level up from a submodule

• i.e., submodule.submodule will work, and
• and package.submodule.submodule will work
• but submodule.submodule.submodule will not work

For example this will work

utils.extract_model_from_parallel
utils.save
utils.wait_for_everyone
utils.set_seed
utils.synchronize_rng_state
utils.install_xla 
utils.load_checkpoint_in_model
utils.load_and_quantize_model
utils.DeepSpeedPlugin
utils.DeepSpeedPlugin.deepspeed_config_process
accelerate.DeepSpeedPlugin.deepspeed_config_process

Also this will work, because it starts from accelerate

accelerate.DeepSpeedPlugin.deepspeed_config_process

But this will not work

utils.deepspeed.DummyOptim

This PR will allow the last example to work

[fabianlim]

Closing because https://github.com/huggingface/accelerate/pull/2729/files seems to address the issue and has been merged. Can be reopened in future if there is interest.