Handle updates for demos

Create a release branch for demos (this might be already done elsewhere). Then update all refs to `main` to be the release branch.

Not all refs, but all github refs.

See also: https://github.com/stackabletech/demos/issues/66

```[tasklist]
### PRs
- [ ] https://github.com/stackabletech/demos/pull/132
- [ ] https://github.com/stackabletech/stackable-utils/pull/91
```