Fix handling of extra_args for ModelBuilder pass

[shaahji]

Fix handling of extra_args for ModelBuilder pass

GenAI model builder's extra_args works based on existence of a key rather then the value of the key itself. So, Olive cannot pass a key with a value of true/false. The key has to explicitly be added/removed based on the value of the key itself in the user config.

Checklist before requesting a review

• Add unit tests for this change.
• Make sure all tests can pass.
• Update documents if necessary.
• Lint and apply fixes to your code by running lintrunner -a
• Is this a user-facing change? If yes, give a description of this change to be included in the release notes.
• Is this PR including examples changes? If yes, please remember to update example documentation in a follow-up PR.

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[jambayk]

nit: this condition is not needed since the value is always a bool and this condition is always true.