[AIT-203] Add example images for AI Transport streaming patterns

[matt423]

Description

This PR adds example images for the AI Transport streaming examples on the examples index page.

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Changes

• Added - Visual representation of message-per-token streaming pattern where each token is sent as a separate message
• Added - Visual representation of message-per-response streaming pattern where tokens are appended to a single message

These images will automatically appear on the examples index page through Gatsby's GraphQL query that matches image filenames to example IDs.

Checklist

• Commits have been rebased.
• Linting has been run against the changed file(s).
• The PR adheres to the writing style guide and contribution guide.

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