Tests for personal tags Webdav

Note: this is NOT system tags.

These are internal personal tags that can be set on files.
Currently this isn't used anywhere and this feature exists since OC 8.1.
The only usage is the special tag used for favorite files.

To test manually: create a file "proppatch-tags.txt":

<?xml version="1.0"?>
<d:propertyupdate xmlns:d="DAV:" xmlns:oc="http://owncloud.org/ns">
  <d:set>
    <d:prop>
      <oc:tags>
        <oc:tag>tag1</oc:tag>
        <oc:tag>tag2</oc:tag>
      </oc:tags>
      <oc:favorite>1</oc:favorite>
    </d:prop>
  </d:set>
</d:propertyupdate>

Then: curl -X PROPPATCH -H "Content-Type: text/xml" --data-binary "@proppatch-tags.txt" http://root:admin@localhost/owncloud/remote.php/files/file.txt

Then create a file "propfind-tags.txt":

<?xml version="1.0"?>
<a:propfind xmlns:a="DAV:" xmlns:oc="http://owncloud.org/ns">
        <a:prop>
                <oc:tags/>
                <oc:favorite/>
        </a:prop>
</a:propfind>

Then check the output of the PROPFIND: curl -X PROPFIND -H "Content-Type: text/xml" --data-binary "@propfind-tags.txt" http://root:admin@localhost/owncloud/remote.php/files/file.txt

<?xml version="1.0"?>
<d:multistatus xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns" xmlns:oc="http://owncloud.org/ns">
 <d:response>
  <d:href>/owncloud/remote.php/files/file.txt</d:href>
  <d:propstat>
   <d:prop>
    <oc:tags>
     <oc:tag>tag1</oc:tag>
     <oc:tag>tag2</oc:tag>
    </oc:tags>
    <oc:favorite>1</oc:favorite>
   </d:prop>
   <d:status>HTTP/1.1 200 OK</d:status>
  </d:propstat>
 </d:response>
</d:multistatus>

Start by preparing the two XML request files shown in the issue and run the PROPPATCH command against the ownCloud WebDAV endpoint. Then run the PROPFIND command and compare its response with the expected XML, confirming that tag1, tag2, and favorite are returned with HTTP 200 OK.