fix app provider "new url" capability

[wkloucek]

Description

Fix of #2884 and cs3org/reva#2379, since "new_url" was added as option, but was not hooked up in the oCIS frontend part...

After this fix we get:

curl -k 'https://localhost:9200/ocs/v1.php/cloud/capabilities?format=json' -u einstein:relativity | jq '.ocs.data.capabilities.files.app_providers'

[
  {
    "enabled": true,
    "version": "1.0.0",
    "apps_url": "/app/list",
    "open_url": "/app/open",
    "new_url": "/app/new"
  }
]

Unblocks owncloud/web#5890

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication