Make PUT and POST operations for repositories Ansible friendly

The PUT and POST operations to `/v1/repository` are unsuitable for automated management with Ansible (_as example_). PUT completely ignores the "uuid" from the body and generates a new one upon successful creation. POST ignores changes of "identifier" although "uuid" being the unique identifier. With this behavior, it is not possible to manage the configuration using Ansible. It would be necessary to DELETE a repo first using its uuid and then create it with PUT. But in this case, the uuid will change and it must be stored in some sort of state-file. That is not how Ansible is meant to be used.

### Proposed Behavior:
- allow changes of "identifier" using POST
- PUT should respect "uuid" from the request body