New sensors for last update and online/offline connection status

[atc99]

Add a new sensor for last update received (datetime) and an online/offline Connection Status. Naming is not fixed and is just a suggestion. Adding these could enable support for other automation notifications or more advanced rules related to load-balancing.

• Last Update (Received)
  • Last time a command was received from the JB
• Last Update (Sent)
  • Last time a command was sent to the JB for a configuration change (current changes, etc)
• Connection Status
  • [Online,Offline] enum.
  • JPP sends offline for all JB's it has been processing commands for when shutting down.
  • JPP calculates this based on how long it has been since the JB was last seen. Should be aligned with the 3-5 minute online/offline charging current setting.

[atc99]

It looks like the last_changed attribute may cover the last update (received) and possibly the sent when using a template variable.

The connection status may also be able to be determined by the last_changed attribute or it could be an automation that updates a manually created sensor based on a last_changed attribute, but having JPP actively update it may be useful.