[PyTorch] Adding TP overlap support for `te.Linear` with `parallel_mode="column"`

[denera]

Description

te.Linear currently only supports TP overlap with parallel_mode="row" where it overlaps reduce-scatter in the forward pass, and all-gather with dgrad in the backward pass.

This PR adds new options to enable all-gather overlap in the forward pass, and reduce-scatter overlap with dgrad in the backward pass, when parallel_mode="column".

Fixes #1312

Type of change

• [ ] Documentation change (change only to the documentation, either a fix or a new content)
• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Infra/Build change
• [ ] Code refractor

Checklist:

• [x] I have read and followed the contributing guidelines
• [x] The functionality is complete
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[denera]

/te-ci pytorch L1