Add endpoint to rename project

Endpoint: `PATCH /api/projects/<id>`

Body:
```json
{
  "name": "New Project Name",
}
```

This endpoint should only allow to rename the project. Conversely, it's not possible to modify other properties such as the id or the task (in fact labels can be edited, but through a different endpoint).

For the implementation, take a look at the other PATCH endpoints for reference.