chore: move existing examples under experimental and add notes example

[adklempner]

Moving forward, we want to focus on maintaining a single flagship example in this repository that is updated with every release of js-waku packages. This will be the notes example from this PR: waku-org/examples.waku.org#286

The other examples should be moved to an experimental folder; we want to retain the code for future reference, as we may implement some of the same features in the notes example or re-introduce them as one of the examples we maintain.