Add Hospital Outpatient Activity

[milanwiedemann]

Overview

@kayleepn discovered (after meeting Orla) that the Hospital Outpatient Activity dataset is also available and we should consider adding it. This would add insights into clinical activity that is currently not captured in any of the datasets available through OpenCodeCounts.

Technical implementation

Adding this dataset should also be very straightforward as the data is in a similar format to all the other files and we should be able to reuse the code from the Hospital Admitted Care datasets.