Side effect

TODO: Document how to safely run side-effects as response to LiveStore events.

Notes for writing those docs:

• Scenarios:
  • Run side-effect in each client session
  • Run side-effect only once per client (i.e. use a lock between client sessions)
  • Run side-effect only once globally (will require some kind of global transaction)
• How to deal with rollbacks/rebases
• Allow for filtering events based on whether they have been confirmed by the sync backend or include unconfirmed events