Allow to disable auto-transactions for stored procedures mapped to CUD operations

[AndriySvyryd]

Some sprocs cannot be executed in a transaction. These need a configuration flag that will affect SaveChanges and the execution strategy.

Current workaround is to use a transaction interceptor.

Split off from #245

[roji]

Another possible workaround would be to set AutoTransactionsEnabled=false, disabling the transaction for the entire SaveChanges.

[roji]

#28711 is replacing AutoTransactionsEnable with a 3-value enum (WhenNeeded, Always, Never), @AndriySvyryd suggested adding a WhenNotInvokingStoredProcedure for this. Some possible drawbacks:

• We discussed possibly only exempting the specific sproc from the transaction in the batch, i.e. wrapping all the other modification commands in transactions, before and after.
  • If we do this, we need specific metadata on the sproc rather than a global AutoTransactionBehavior setting.
  • This is maybe of somewhat limited value, because if there's a failure there's still the possibility of inconsistency. This would only reduce the change of an inconsistency (i.e. only if the failure occurs occurs inside or after the sproc).
• This would require users to manually set AutoTransactionBehavior everywhere where the specific sproc is being used. Specifying this once in metadata would be a better user experience.