[oc] Enable chunking for bigger files in authenticated web upload

[danxuliu]

Imported from owncloud/core#28415.

This pull request adds chunked uploads in the Web UI (for authenticated users, but not for public uploads). To do that the server endpoint used by the uploader is changed from WebDAV v1 to WebDAV v2. The chunking itself is done automatically by the jQuery-File-Upload plugin when the maxChunkSize parameter is set; in fileuploadchunksend the request is adjusted to adapt the behaviour of the plugin to the one expected by uploads/ in WebDAV v2.

The chunk size to be used by the Web UI can be set in the max_chunk_size parameter of the Files app configuration. By default it is set to 10MiB.

Differences with the original pull request:

• port is not removed; removing it is not needed for the other changes (it was just an unrelated cleanup due to the port being already included in host), and it could be needed by some user of the client object, so it feels safer to keep it.
• core/js/config.php was removed in Remove config.php for oc.js #1961 after its functionality was replaced with lib/private/Template/JSConfigHelper.php; the changes are not needed in the new code.
• apps/files/lib/App.php was adapted due to the settings array now (after the configuration changes mentioned above) being encoded in JSON instead of being a plain PHP array.

This pull request (like the original one, if I am not mistaken) is not bug free. If an upload is cancelled it is not possible to upload other files until the page is reloaded, and there are also some issues with the progress bar when several files are uploaded at once and one of them fails.

However, I would prefer to merge this as is now and fix the bugs later to be able to import other pull requests based on this one in an easier way.

[codecov]

Codecov Report

Merging #7056 into master will decrease coverage by <.01%.
The diff coverage is 45.45%.

@@             Coverage Diff              @@
##             master    #7056      +/-   ##
============================================
- Coverage     50.61%   50.61%   -0.01%     
- Complexity    24297    24298       +1     
============================================
  Files          1577     1577              
  Lines         92922    92931       +9     
  Branches       1359     1359              
============================================
+ Hits          47036    47040       +4     
- Misses        45886    45891       +5

Impacted Files	Coverage Δ	Complexity Δ
apps/files/appinfo/app.php	100% <ø> (ø)	0 <0> (ø)	⬇️
apps/files/lib/App.php	17.64% <0%> (-9.63%)	3 <1> (+1)
core/js/files/client.js	83.02% <100%> (+0.15%)	0 <0> (ø)	⬇️
apps/files_trashbin/lib/Trashbin.php	72.53% <0%> (+0.24%)	136% <0%> (ø)	⬇️

[MorrisJobke]

Tested and works 👍

[blizzz]

Tested, works +1