Add support for PROPPATCH HTTP method for custom properties of file and directory

[hci2]

It would be nice to add support for PROPPATCH HTTP method to add custom properties to a directory or file.

The way to do this is described in that article for the custom property invoicenumber: https://mathiasconradt.medium.com/how-to-assign-custom-meta-data-to-your-documents-on-nextcloud-23356cf3f926

There is also a half-working (stale) Nextcloud App for that: https://apps.nextcloud.com/apps/customproperties

It would be possible to allow an extraProperties (https://github.com/tentwentyfour/nextcloud-link#webdav-extraproperties) parameter as optional (extraProperties?: FileDetailProperty[]) to the uploadFromStream, put, touchFolder or createFolderHierarchy methods of the client.

The equivalent "PROPFIND HTTP method is not essentially needed because a similar result can be achieved via getFolderFileDetails method and the extraProperties property.

What do you think about that extension?