Added api/classifications endpoint, requiring a new query

internal/store/queries_test.go

@@ -100,6 +100,9 @@ var checks = map[string]queryCheck{
 	"insertOpportunityClassification": {
 		sql: insertOpportunityClassification,
 	},
+	"selectClassificationsInUse": {
+		sql: selectClassificationsInUse,
+	},
 	"selectClassificationsForOpportunities": {
 		sql: selectClassificationsForOpportunities,
 		in:  true,