add sessions without needing to do export/replace all bookings #32
Description
as per practable/admin-tools#10, having to export/replace bookings causes several potential issues, at least including
- closure of bookings for a short period
- additional fixes in data to correct audit trail, or lose track of user time in current sessions when booking updated
- unfairly charging for an extra session start (may be relevant when there is a lot of setup cost incurred for each booked session, e.g. loading chemicals, using a finite resource from a hopper/supply belt etc)
It would be better to allow an add-booking route that bypasses the need for the user to have a group that permits them access to the policy, so that sessions can be added WITHOUT also giving the session recipient the right to book again
Such an endpoint would need to respect the other booking checks.
Would also need to be protected by credentials as per other admin routes
We need this regardless of what backend we have - we'd have to take this approach before we could have this feature on a database supported system, for example, because modifying the database directly would not update the in-memory trees that book uses to be efficient in accepting/rejecting bookings.