[EF] Connection resiliency

- connection retry policy
- works great with async
- four modes
    - DefaultExcutionStrategy
    - DefaultSqlExecutionStrategy
    - DbExecutionStrategy
    - SqlAzureExecutionStrategy
- throws RetryLimitExceededException

##Configuration

public class MyConfiguration : DbConfiguration 
{ 
    public MyConfiguration() 
    { 
        SetExecutionStrategy("System.Data.SqlClient", 
        () => new SqlAzureExecutionStrategy(1, TimeSpan.FromSeconds(30))); 
    } 
}

MSDB

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