change the create dist job functionn to support creating a single nod…

[delgadof]

This pull request refactors the create_distributed_job method to a more general-purpose create_training_job method in the DGXCloudExecutor class, improving functionality and clarity. It also updates related test cases to align with the new method.
closes #239

Core functionality changes:

• Renamed create_distributed_job to create_training_job in nemo_run/core/execution/dgxcloud.py, adding support for both single-node and multi-node training jobs on DGX Cloud. The method now validates inputs, determines the appropriate endpoint based on node count, and constructs payloads accordingly.
• Updated the launch method to call the new create_training_job method instead of the old create_distributed_job.

Test updates:

• Renamed and updated the test method test_create_distributed_job to test_create_training_job in test/core/execution/test_dgxcloud.py to reflect the new method name. [1] [2]
• Updated test cases that previously mocked create_distributed_job to mock create_training_job instead, ensuring compatibility with the refactored method. [1] [2]

[delgadof]

Modified the formatting to meet the repository requirements

[roclark]

LGTM! do we also want to add a test for launching a single-node job to ensure it goes down the single-node path in create_training_job? Thanks for putting this together!

[delgadof]

@roclark You are right. commit 7962d92 add these features.

[roclark]

Awesome work, thanks!!