cosmos db entra id support and fixes

[TheovanKraay]

Add support for Entra ID in the auto config for Azure Cosmos DB vector store support.
This PR also adds a few fixes/enhancements and corresponding tests:

• fix to ensure getMetadata() returns the metadata fields and values
• allow metadata field to be defined as the Cosmos DB partition key (and not just /id)
• allow choice between gateway and direct mode in autoconfig

[sobychacko]

@TheovanKraay As @markpollack commented on the other issue, we could not verify certain refactoring changes we made due to the lack of access to a proper CosmosDB environment. Apologies for that bug you mentioned. Quick question: Did you get a chance to verify all the tests including the IT's on yoru CosmosDB environment? Thanks!

[TheovanKraay]

@TheovanKraay As @markpollack commented on the other issue, we could not verify certain refactoring changes we made due to the lack of access to a proper CosmosDB environment. Apologies for that bug you mentioned. Quick question: Did you get a chance to verify all the tests including the IT's on yoru CosmosDB environment? Thanks!

For this PR I have run all the ITs and they pass (using Entra ID with appropriate level of access to the Cosmos DB resources).