Spring-ai Fixing MongoDB vector store support test failures

Remove the requirement of MongoDB vector store auto-configuration only after MongoDataAutoConfiguration. This enables the MongoDBAtlasVectorStoreAutoConfiguration to properly provide custom Mongo conversions.

In MongoDBAtlasVectorStoreIT and MongoDbVectorStoreObservationIT tests, properly provision the MongoTemplate with custom conversions as these tests are not relying on auto-configuration.

Comment From: tzolov

This is great! Thanks @sobychacko !

Comment From: rozza

@tzolov & @markpollack I think you can probably close out #1022.

It took an alternative approach of adding a single MimeTypeConverters class which was used by both MongoDBAtlasVectorStoreAutoConfiguration and in MongoDBAtlasVectorStoreIT. Although I think the TestApplication in #1022 is much simplier / more readable.