Setpoint 2716 grid setpoint

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Victron recommends: VE.Bus ESS systems: add register 2716, setting volatile AC power setpoint. All systems doing frequent updates of the power setpoint, ie. systems having their own control loop, are recommended to use register 2716 instead of registers 2700 and 2703. The difference is that 2716 is a volatile setting, and doesn’t result in writes to (settings-) log files.
Add an address 2716.