Add more examples using transactions in different ways

In the section *Execution strategies and transactions* two BlogginContext are created in the first sample code. Why is this necessary? I’ve tried to use only one and that seems to work fine. In similar code on this blog only one database context is used: https://devblogs.microsoft.com/cesardelatorre/using-resilient-entity-framework-core-sql-connections-and-transactions-retries-with-exponential-backoff/

Also, if two BloggingContext are necessary I think the samples are a bit to simplified. I guess that in most real applications the first BloggingContext is created from dependency injection. How do we properly create the second one?

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* ID: 876c88d4-2972-d905-28d7-56f9e589f309
* Version Independent ID: 29002343-fa42-2f49-3362-53592039b26d
* Content: [Connection Resiliency - EF Core](https://docs.microsoft.com/en-us/ef/core/miscellaneous/connection-resiliency#feedback)
* Content Source: [entity-framework/core/miscellaneous/connection-resiliency.md](https://github.com/aspnet/EntityFramework.Docs/blob/master/entity-framework/core/miscellaneous/connection-resiliency.md)
* Product: **entity-framework**
* Technology: **entity-framework-core**
* GitHub Login: @rowanmiller
* Microsoft Alias: **divega**