Add OpenAI APIs to missingapi.yml file

[gewarren]

Add missing OpenAI APIs to https://github.com/dotnet/dotnet-api-docs/blob/main/_zip/missingapi.yml, similar to

dotnet-api-docs/_zip/missingapi.yml

Lines 34 to 37 in 5bc6ad4

	- uid: OpenAI.Assistants.AssistantClient
	name: AssistantClient
	fullname: OpenAI.Assistants.AssistantClient
	href: https://github.com/openai/openai-dotnet/blob/main/api/OpenAI.netstandard2.0.cs

.

Recent build warnings in the xml/Microsoft.Extensions.AI/OpenAIClientExtensions.xml file:

Line 0: [Warning] Cross reference not found: 'OpenAI.Assistants.FunctionToolDefinition'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Chat.ChatTool'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Realtime.ConversationFunctionTool'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Responses.ResponseTool'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Assistants.FunctionToolDefinition'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Assistants.FunctionToolDefinition'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Chat.ChatTool'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Chat.ChatTool'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Responses.ResponseTool'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Responses.ResponseTool'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Realtime.ConversationFunctionTool'.
Line 0: [Warning] Cross reference not found: 'OpenAI.Realtime.ConversationFunctionTool'.

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Associated WorkItem - 454761