Improve guidance on transactions, uow, and partial updates

[ramonsmits]

Based on livechat:

Improve the doco on partial updates to explain why it is good to have all handler share a single transaction and to have a single incoming message that invokes multiple handler to be one unit of work (uow).

• https://docs.particular.net/transports/transactions

Make sure that this is linked from transports like RabbitMQ that by default do not use TransactionScope and can cause partial updates and that WrapHandlersInATransactionScope can be used to prevent this.

Explain that when there is a need to run handlers in isolation that a better pattern is to split up the work in separate messages where each messages is processed in its own transaction.