Add probe part number to the probe annotations

[bparks13]

Due to changes in how probe metadata is being extracted and saved in ProbeInterface (see here), it would be beneficial if we saved the probe part number in the probe. Specifically, we can add it to the ProbeAnnotations class, which follows the JSON schema by allowing additional fields beyond what is explicitly defined.

It would probably be best to make this change in the OpenEphys.ProbeInterface.NET repo, where the property can be marked as optional, and then utilize it in this repo.