refactor: add @filterable tag to filterable properties

src/things/date-series.ts

@@ -47,6 +47,8 @@ export interface SCDateSeriesWithoutReferences
   extends SCThingThatCanBeOfferedWithoutReferences {
   /**
    * Dates of the date series that are initially planned to be held
+   *
+   * @filterable
    */
   dates: SCISO8601Date[];