Synology DSM: add device_class: safety, and change sensor to binary sensor

using the current integration, it would be nice if the binary_sensors for exceeded_max_bad_sectors and below_min_remaining_life use the device_class: safety.

also, we now have a regular sensor for status per drive, which could also be made into a binary_sensor, and again use the device_class: safety.

it would prevent us to have to use customizations like:

    binary_sensor.diskstation_*:
      templates:
        icon: >
          if (state == 'on') return 'mdi:alert-circle';
          return 'mdi:check-circle';

for showing correct icons in the frontend.