Make checksum propfind future proof

[rullzer]

The checksum PR from #21997 returns a propfind like:

<oc:checksum>TYPE:CHECKSUM</oc:checksum>

Which if we will ever support multiple cheksums results in:

<oc:checksum>TYPE1:CHECKSUM1,TYPE2:CHECKSUM2</oc:checksum>

Which is not very webdavvy.

This PR moves that to:

<oc:checksums>
  <oc:checksum>TYPE1:CHECKSUM1</oc:checksum>
  <oc:checksum>TYPE2:CHECKSUM2</oc:checksum>
</oc:checksum>

Which is a bit more future proof.

Testing is basically the same as: #21997 (comment) with the exception that your propfind file should contain:

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

CC: @PVince81 @dragotin @MorrisJobke @nickvergessen

[mention-bot]

By analyzing the blame information on this pull request, we identified @PVince81, @DeepDiver1975 and @LukasReschke to be potential reviewers

[MorrisJobke]

(multiple_checksums) $ curl -u mjob:mjob -X PROPFIND http://localhost/master/remote.php/webdav/foobar --upload-file prop
<?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>/master/remote.php/webdav/foobar</d:href>
  <d:propstat>
   <d:prop>
    <oc:checksum/>
   </d:prop>
   <d:status>HTTP/1.1 404 Not Found</d:status>
  </d:propstat>
 </d:response>
</d:multistatus>
(multiple_checksums) $ git checkout master                                                                                       
Switched to branch 'master'
Your branch is up-to-date with 'origin/master'.
(master) $ curl -u mjob:mjob -X PROPFIND http://localhost/master/remote.php/webdav/foobar --upload-file prop
<?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>/master/remote.php/webdav/foobar</d:href>
  <d:propstat>
   <d:prop>
    <oc:checksum>MD5:12i34769781236496913,sha1:asdoöiadshfölha</oc:checksum>
   </d:prop>
   <d:status>HTTP/1.1 200 OK</d:status>
  </d:propstat>
 </d:response>
</d:multistatus>

[MorrisJobke]

@rullzer Seem to be broken. :(

[MorrisJobke]

Tested with the updated file prop and it works now 👍

[karlitschek]

I'm O.K.with that. But please discuss architecture question like that with @DeepDiver1975 and me in the future.
👍