docs: def get_applied_migrations(databases=None):
      """
      Returns a dictionary containing lists of all applied migrations
      where the key is the database alias.
      """
      if not databases:
          databases = get_capable_databases()
      else:
          # We only loop through databases that are listed as "capable"
          all_databases = list(get_capable_databases())
          databases = list(
              itertools.ifilter(lambda x: x in all_databases, databases)
          )
      
      results = defaultdict(list)
      for db in databases:
          for x in Migration.objects.using(db).order_by("migration_label"):
              results[db].append(x.migration_label)
      
      return results