[!!!][BUGFIX] Skip automatic persistence for updated entities
When trying to persist changes in a "safe request" (e.g. ``GET``) Flow
throws an exception::
Detected modified or new objects [...] to be persisted which is not
allowed for "safe requests"
including details on how to work around this.
This currently only works if entities have been added or removed.
With this change also updates to entities are tracked correctly so
that automatic persistence is skipped for modified objects for safe
This is a breaking change when code relied on the incorrect behavior of
automatically persisting changes even for safe requests.
In this case make sure to trigger updates only via unsafe requests (e.g.
``POST`` or ``PUT``).
If that's not an option, the issue can be worked around with a manual
call to ``PersistenceManager::persistAll()``.