Cosmos: allow to specify a custom Json serializer and serialization options

[alexeymarkov]

I am trying to make EF Core Cosmos provider working with camel case json but I could not find a way how to do it.
I could probably resolve SingletonCosmosClientWrapper, call Client property and assign SerializerOptions but this would not give me a possibility to provide a custom Json serializer if I want.
And I do not want to bind each property of each my entity with JsonProperty attribute or to call ToJsonProperty for all of them.

Somewhere in UseCosmos.

[AndriySvyryd]

Duplicate of #17306