Create function include_podiatrist_services()

[signekb]

Based on the functionality flow, this function should filter diabetes-specific podiatrist services from health service register data to create the diabetes cohort.

osdc/vignettes/function-flow.Rmd

Lines 100 to 105 in 375e652

	### Diabetes-specific podiatrist services
	The function `include_podiatrist_services()` uses `sysi` or `sssy` as
	input to extract the dates of all diabetes-specific podiatrist services.
	<!-- TODO: Add details on how this filtering should be done -->

From @Aastedet 's original issue on this function #9 :

The function should be able to process data with different time-stamps (date or week&year). Some users may have data on HONUGE/HONAAR (which week & year the service was billed by the clinic to the health insurance) and others may have data on the exact date the services was registered.

[lwjohnst86]

Include logic in algorithm.csv as well