[jenkins] Add provisioning_api app

Issue to track the addition of the provisioning_api to the core.

Fixes self.

Todo:
- [ ] Check unit tests
- [ ] Check merge situations (with existing core routes)
- [ ] key has to be added in here https://github.com/owncloud/documentation/blob/master/go.php#L12
- [ ] please follow naming convention 'admin-provisioning-api'
as documented by @tomneedham 
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This extends the existing method in core. Created new issue to track the cleanup of this: #13002