Update server `syncFrequency` value to match client `sync_frequency`
Update server `syncFrequency` value to match client `sync_frequency`

Currently the server-side dataset sync frequencies are set to 10 seconds
whereas the client-side dataset sync frequencies are set to 5 seconds.

Having differing sync frequencies can cause unnecessary load on the
server, causing a full sync to be performed twice for each server-side
sync loop frequency.

This change adds the `syncFrequency` option which will default all
server-side datasets to sync every 5 seconds also.

The multiple sync issue has been documented from the following two
issues:

* FH-3018
* FH-3062

feedhenry-raincatcher/raincatcher-demo-cloud