Json-serialization using a single serializer

[carl-berg]

Currently CosmosDbCollection uses both DocumentClient and Container to access the database. These api's use different serialization options which means sometimes the configured Json.NET settings (date-handling etc) are used and sometimes they aren't. I assume both api's are currently used to support bulk operations. Hopefully that is no longer needed: https://docs.microsoft.com/sv-se/azure/cosmos-db/how-to-migrate-from-bulk-executor-library and we can use just the Container where serialization can be replaced when creating the CosmosDbClient.
Interestring links:

• Add support for JSON.net JsonSerializerSettings Azure/azure-cosmos-dotnet-v3#551
• https://docs.microsoft.com/sv-se/azure/cosmos-db/how-to-migrate-from-bulk-executor-library