Cancellation Token support for Async transaction methods

[dje1990]

Hi,
Regarding in the class Database.cs the methods BeginTransactionAsync(), AbortTransactionAsync() and CompleteTransactionAsync().
Thank for you implementing these methods.
Is it possible to pass through a cancellationToken to the underlying DbConnection methods?
BeginTransactionAsync() already has an overload that takes a cancellationToken as a parameter, but the method does not pass this cancellationToken to DbTransaction.BeginTransactionAsync().
AbortTransactionAsync() and CompleteTransactionAsync() do not have overloads that take a cancellationToken as a parameter, but could pass one to CleanupTransactionAsync(), which could then pass the cancellationToken to DbTransaction.CommitAsync() and DbTransaction.RollbackAsync().

Thanks for your help.

Related to:
#629
#628

[Ste1io]

I noticed the same thing when working on the doc comments; check the branch for #682 and you'll see I added inline to-do comments and put it on the list of fixes for once that PR is merged.