Support MongoDB's read/write concerns by the following approach:

1. injected Mongo-specific `MongoSessionFactory` which is a wrapper of existing Hibernate's default `SessionFactory` with additional read/write concerns config
2. Injected Mongo-specific `MongoSession` which is a wrapper of existing Hibernate's default `Session` with additional read/write concerns config
3. add overloaded methods for both `MongoSessionFactory` and `MongoSession` to provide explicit read/write concern config when creating `Session` (from `MongoSessionFactory`) or `Transaction` (from `MongoSession`), which will overwrite the default config of the initiator (`MongoSessionFactory` and `MongoSession`)
4. use `ThreadLocalCurrentSessionContext` to bind the newly-created `MongoSession` to the context
5. getting the `TransactionOptions` stored in the `current session` above from `MongoConnection` when a new transaction is to be created.