Add release management

In many companies, there is lifecycle around models. Especially in safety critical applications, release management is a very important topic.

There has to be release management functionality in the Collab Manager. In general, the following should be implemented:
- [ ] A specific version of a model should be tagged with a version. In the beginning, we could use Git tags as representation of the version. The management of the Git tags should take place in the Collab Manager.
- [ ] A specific version should be approved by specific roles (#71).
- [ ] There may be artifacts related to specific tags. Users should be able to upload files manually or use documentation generation to generate specific files (#68).