Add support for embedding dimensions and fix prepdocs on Windows

[mattgotteiner]

Purpose

• Add support for embedding models with the dimensions parameter in Azure OpenAI
• Fix prepdocs runs on Windows

Does this introduce a breaking change?

[ ] Yes
[X] No

Pull Request Type

What kind of change does this Pull Request introduce?

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

How to Test

• Set AZURE_OPENAI_EMBEDDING_MODEL_DIMENSIONS and another embedding model (e.g. text-embedding-3-large) that supports other types of dimensions
• Run ./scripts/prepdocs.ps1 on Windows

What to Check

Verify that the following are valid

• The container app does not crash when you chat with it
• You can upload new documents without crashing
• The index has the correct embedding dimensions