Expose choice when there are multiple adjustment sets

[christopher-wild]

Currently when multiple viable minimal_adjustment_sets are found, the smallest one is chosen programmatically.

There are reasons however for the user to consider another minimal_adjustment_set more suitable and may wish to have a choice between the different adjustment sets. One reason for example is there could be much better data for nodes of one adjustment set over another.

After a discussion with @jmafoster1 and @AndrewC19 on 25/10/22, it may be most appropriate to add two new parameters to the identification function or to the execute_test_suites function (to be decided).

The first parameter would be a flag to indicate that the code should be halted when multiple adjustment sets are found and displaying the multiple minimal_adjustment_sets. This would give the user chance to explore and decide which adjustment set is most appropriate.

The second parameter would be a mechanism for pre-selecting an adjustment set if the user already knew from previous executions which set was most appropriate.

[christopher-wild]

also look at #58

[jmafoster1]

Might be worth adding this to the test output? E.g. a field with the adjustment set that was actually used and another field for the other adjustment sets that it found that could have been used instead. The only issue here is that, for complex DAGs, it might find a lot of adjustment sets which could clog up the logs, but since it's all just JSON, I guess you could filter it out easily if you didn't want it.