Investigate uploadFile option overwrite capability

[eblondel]

To look at both owncloud and nextcloud impls.
This relates to OwnCloud user request eblondel/ownCloud4R#8

[eblondel]

A first attempt was to add a delete_if_existing parameter (default = FALSE).

The overwrite logic has to be further studied in key cloud solutions like OwnCloud and NextCloud. the latter (Next cloud) seems to indicate that overwrite is the default behaviour (pending question of how resources shared with public links are then treated, if link is conserved or not). In the former (ownCloud) , the overwrite is not possible by default, and we get an error when attempting to reupload some file. This may be due to the fact the Owncloud UI asks the user what to do when re-uploading a file, between overwriting or keeping a separate copy of the file.
In the case of OwnCloud, the delete_if_existing can be set to true, having similar result as the overwrite, to answer some basic use case, but with the limit that if the previous file was shared with a public link, this link will be probably lost, because the file is first deleted to be then reuploaded as new resource.

[eblondel]

In nextcloud, this should work if we catch well http status code 204 (no content). Commit to follow cc @wheintz

[eblondel]

Guys, this seems solved according to the latest fix and test done. I've included the HTTP code 204 (no content) as acceptable for upload, and the test performs 2 successive uploads, both successful!