Handle redirect to current slug

[leafty]

When a slug is updated in Renku 2.0, the old slug can still be used for GET queries (until it is claimed). In such cases, the UI should handle updating the browser URL to the new one.

Example:

1. Create a group, with slug example-group.
2. Update the group with a new slug example-new-group.
3. Manually load the group page with the old slug example-group.

The UI should change the URL to example-new-group but does not at the moment. Note that this should happen for groups, users, projects, etc.

[leafty]

Note: maybe the API should reply with a 3xx response instead?