fix: Allow rank differences in aten.expand

[gs-olive]

Description

• Add support for aten.expand.default in Dynamo converter registry
• Build converter to support rank-padding for input Tensors, in line with the existing Torch behavior
• Add test case to validate new behavior, in addition to existing cases validating old behavior

Fixes #2183

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• [ x ] My code follows the style guidelines of this project (You can use the linters)
• [ x ] I have performed a self-review of my own code
• [ x ] I have commented my code, particularly in hard-to-understand areas and hacks
• [ x ] I have made corresponding changes to the documentation
• [ x ] I have added tests to verify my fix or my feature
• [ x ] New and existing unit tests pass locally with my changes
• [ x ] I have added the relevant labels to my PR in so that relevant reviewers are notified

[apbose]

As such the changes look good. But I think this was already taken care in the slice/ops.py. This condition was getting encountered in aten::where cases where the two inputs were not of equal dimensions. However since there was no aten.ops.expand in dynamo, it was picking up the acc_ops implementation. Its good that a test case for this in expand has been added.
We should either keep this or the slice one, and accordingly change the call to expand elsewhere.

[gs-olive]

Thanks for the comments and suggestions. I have merged the implementations into one expand implementation now, which is in slice/ops.

[narendasan]

LGTM