enable full passthrough of vllm engine args, with backwards compatibi…

[siddvenk]

…lity for existing differences with engine agnostic configs

Description

This PR addresses a common pain point with using vllm. We currently restrict the set of engine args that can be passed based on what we expose through VllmRbProperties. This change does the following:

• enable pass through args via Pydantic extra configs
• remove configs from VllmRbProperties that are exactly the same as the vllm engine args in both name and default value
• validate specific configs that we have different engine agnostic names for

Raising this in draft if people want to start looking and providing feedback. I have the following TODOs still:

• Add unit tests for the properties class to test this change in behavior
• Add documentation updates to instruct customers on how to use this change correctly

I plan on making a similar change for LMI-Dist. I'm starting with VLLM first to keep the change contained, and gather feedback suggestions which I'll take forward for LMI-Dist.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist:

• Have you manually built the docker image and verify the change?
• Have you run related tests? Check how to set up the test environment here; One example would be pytest tests.py -k "TestCorrectnessLmiDist" -m "lmi_dist"
• Have you added tests that prove your fix is effective or that this feature works?
• Has code been commented, particularly in hard-to-understand areas?
• Have you made corresponding changes to the documentation?

Feature/Issue validation/testing

Please describe the Unit or Integration tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
Please also list any relevant details for your test configuration.

• Test A
  Logs for Test A

• Test B
  Logs for Test B