Add information about occupancy rate (% at a certain date)

Problem description
Some key indicators for the transaction of investment properties are missing in SwissRETS.

Desired Solution
A way to indicate the occupancy rate (i.e. the rented out area at a certain date / the total area)

This would require an option to indicate the percentage, and an option to indicate the reporting date.

[jensstalder]

@rgutzwiller

Something like this?

Just a rough example.

<property>
  <occupancyPercentages>
      <occupancyPercentage year="2020">70</occupancyPercentage>
      <occupancyPercentage year="2019">60</occupancyPercentage>
  </occupancies>
</property>

@jensstalder
There needs to be a way to link the percentage information to a certain day (not year)
Let's say: On the 22.09.2020 the occupancy percentage was at 93%

[jensstalder]

This could eventualy also work if only a single value is required at a date.

<property>
    <occupancyPercentage date="2020-01-01">70</occupancyPercentage>
</property>