change: allow additional model server configuration options

[laurenyu]

Issue #, if available:

Description of changes: This change allows for extra model server options to be overridden. There will be a corresponding Python SDK change for exposing this.

Testing done: unit tests

Merge Checklist

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General

• [x] I have read the CONTRIBUTING doc
• [x] I used the commit message format described in CONTRIBUTING
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Tests

• [x] I have added tests that prove my fix is effective or that my feature works (if appropriate)
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[laurenyu]

closing for now - going to take a different approach