Add Image Input Sample

[kaylieee]

Purpose

• Add new sample for Image Input that streams responses from OpenAI Assistant to an HTML/JS frontend using Server-Sent Events (SSEs).
• Fix issues with sending attachments in multiple messages
• Version updated to 0.4.2-alpha

Does this introduce a breaking change?

[ ] Yes
[X] No

Pull Request Type

What kind of change does this Pull Request introduce?

[X] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[X] Other... Please describe: Sample

How to Test

• Sample README.md
• Run pytests in sdk/azure-ai-assistant/test

Other Information

• Please install new version azure_ai_assistant-0.4.2a1-py3-none-any.whl for middleware SDK from this release. See the README for installation details.