The sync group for this device.
When peer-to-peer transports are enabled, all devices with the same App ID will
normally form an interconnected mesh network. In some situations it may be
desirable to have distinct groups of devices within the same app, so that
connections will only be formed within each group. The syncGroup parameter
changes that group membership. A device can only ever be in one sync group, which
by default is group 0. Up to 2^32 distinct group numbers can be used in an app.
This is an optimization, not a security control. If a connection is created
manually, such as by specifying a connect transport, then devices from
different sync groups will still sync as normal. If two groups of devices are
intended to have access to different data sets, this must be enforced using
Ditto's permissions system.
Part of TransportConfig type, settings not associated with any specific type of transport.