Add domain to drug mapping level table

[MaximMoinat]

In some datasets the drug exposure table is very 'dirty', with drug_concept_id's from other domains. This can give a long list of different classes in the Drug Mapping Level table (section 4.4, table 6), making hard to interpret. See example below.

I propose to filter the mapping level query by the drug domain (domain_id = 'Drug'). The only caveat is that this hides that there are concepts from other domains. Although it is the purpose of the DataQualityDashboard to flag those quality issues.