[BT] Device Tracker sync across gateways

[DigiH]

Device Tracker sync across gateways - OpenMQTTGateway & Theengs Gateway, to avoid intermittent AWAY statuses

Checklist:

• The pull request is done against the latest development branch
• Only one feature/fix was added per PR and the code change compiles without warnings
• I accept the DCO.

[bcutter]

Great. If this works out as expected, the provided device_tracker entities (for usage in Home Assistant) can finally start to be practically used. Reaaaally looking forward to see this merged into and shipped with a final release, as the current massive away/home/away/home behaviour renders the whole purpose of device tracking useless. A real milestone.

[1technophile]

Thanks for the PR.
This is going to be integrated but we have some lifting to do before and also the scope of the feature may be extended.

[DigiH]

Closing for the inclusion of
#2094

[bcutter]

https://github.com/1technophile/OpenMQTTGateway/tree/Device-tracker-sync-mod gives a 404.

[DigiH]

@bcutter

#2094