Azure AI Search: Add support for batching save operations

[marcominerva]

Motivation and Context (Why the change? What's the scenario?)

Add support for batch support in Azure AI Search and SaveRecordsHandler.

High level description (Approach, Design)

• New KernelMemory:DataIngestion:MemoryDbUpsertBatchSize setting (default: 1) to manage memory records batch size.
• Implement the new optional IMemoryDbBatchUpsert interface in AzureAISearchMemory.
• Fix old bug in AzureAISearchMemory occurring when EmbeddingGenerationEnabled is false.

[dluc]

A few asks:

• We need to ship the Abstractions nuget with the new interface, before we can use it in other places. We'll need a separate PR focused only on the "Abstractions" project changes, merge it, release the nuget, etc.

• I would prefer splitting the two interfaces, not using inheritance, e.g. class AzureAISearchMemory : IMemoryDb, IMemoryDbBatchUpsert

• 'UpsertAsync' can be refactored to use BatchUpsertAsync, avoiding duplicate code

• I would rename the new interface to IMemoryDbBatchUpsert and the method to BatchUpsertAsync

• I believe some code is missing in the handler, see comment

[dluc]

I added and released the new interface, you should be able to move forward with this PR without creating another one

[dluc]

next steps:

• rebase on latest main (I tried and there's a lot of conflicts, so I'll need more time)
• check exceptions handling
• manual tests