[PyTorch/C] Exposed Userbuffers configuration option to control comm and compute stream priorities

[denera]

Description

Userbuffers configuration dictionary now has new "comm_priority": -1 and "gemm_priority: -1 options with default values of -1 for both.

Attn. @rachitgarg91

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

Changes

• Updated tex.UbufCommOverlap and tex.UbufP2PCommOverlap constructors with optional arguments for comm and GEMM stream priorities.
• Updated te.module.base.initialize_ub() to read "comm_priority" and "gemm_priority" options in the config dictionary.

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