.NET Aspire + Azure OpenAI demo app

Currently a WIP, best to ask me for how to run it locally, but here's the general idea:

• Create an Azure OpenAI resource with a gpt-35-turbo model and a text-embedding-ada-002 model
• Create an Azure AI Speech resource (optional - disable by setting Speech:Enabled to false in appsettings.json)
• Create an appsettings.Development.json file in the AppHost project and populate the details from Azure Resources as per the empty ones in the appsettings.json
• Launch the app, navigate to the frontend -> management screen
• Wait for podcasts to load, choose the one(s) to index and click the Index Selected Items button
• Wait for a bunch of time (no UI progress, but you can click the "Retrieve Status" button to see the indexing status)
• Once indexing is done, go to the frontend / index, enter a prompt and see what happens