Add "password" parameter to the response data of link shares

Due to legacy reasons the password of link shares was returned in the
"share_with" and "share_with_displayname" parameters of the response
data. Now a proper "password" parameter is returned too; the old
"share_with" and "share_with_displayname" parameters are kept, although
deprecated, and they will be removed in a future version of Nextcloud.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>