Updating attachment assignment to use OpenAI Assistant routing

[kylebunting]

Updating attachment assignment to use OpenAI Assistant routing

The issue or feature being addressed

Image files are not being routed as attachments to the Assistant API correctly.

Details on the issue fix or feature implementation

Changing the logic to ensure image attachments are routed correctly to the Assistant API. This change reflects a recent change allowing images files to be passed to the Assistant API with a purpose of vision made in the Python SDK.

Confirm the following

• [x] I started this PR by branching from the head of the default branch
• [x] I have targeted the PR to merge into the default branch
• [ ] I have included unit tests for the issue/feature
• [x] I have included inline docs for my changes, where applicable
• [x] I have successfully run a local build
• [ ] I have provided the required update scripts, where applicable
• [ ] I have updated relevant docs, where applicable

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