Slots need to be fetched by Provider

[kchapple]

https://gponline-fhir.vu2vu.com/fhir/Slot?provider=4&date=lt2020-09-30&date=gt2014-08-30

The provider value in the query string needs to be used to map a provider in the auth providers table to the user in the LibreEHR database. The Slot query should only retrieve slots for the specified provider in the LibreEHR database.

1- process provider in query string
2- fetch the provider out of the auth database
3- After fetching the provider out of auth database, we have their emr_id
4- Use emr_id to filter available slots so only the specified provider's slots are returned

[Leo24]

Add mapping for provider Id
LibreHealthIO/lh-ehr-api#30