Having DavObject::etag property writable

[georgehrke]

@skjnldsv Can you please elaborate again why https://github.com/nextcloud/cdav-library/blob/master/src/models/davObject.js#L57 should be writable here?

Etags are only ever generated on the server and can't be set by the client. And updates will only work if the etag in the If-Match header is correct.

Thx :)

[skjnldsv]

Of course :)
Example:

1. I open a tab with contacts and click the first contact
2. I open the another one and edit the same contact with a random change
3. Back on the first tab, edit the contact
4. A popup will appear stating a change have been detected on the server and you need to click a button to resync the updated contact and that what you did will be discarded (this is a nice ux behaviour, no data loss, clear explanation)
5. we retrieved the etag on the last sync attempt (denied since etag obsolete) so we can manually update the cdav-contact object to specify the new etag manually and trigger a new fullFetch to update everything :)

[skjnldsv]

@georgehrke is it clear? 🙈
If you need a precise example, this is exactly here:
https://github.com/nextcloud/contacts/blob/134527baa933af63400c285b362d9ed889abb001/src/store/contacts.js#L281
We then use this conflict saved etag to update the dav scope linked to the vcard and force a ful refresh :)