Add is_connected api for expansion \w @Willy-JL

[HaxSam]

What's new

• Added new API to expansion to get the information if an expansion is initialized
• The expansion_worker communicates back to the control if there is an RPC connection
• new state for expansion for an established connection

@Willy-JL was heavily involved

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For the reviewer

• I've uploaded the firmware with this patch to a device and verified its functionality
• I've confirmed the bug to be fixed / feature to be stable

[HaxSam]

Still need to add a better comment in expension.h but is nicer to view the changes here to see if I overlooked something at code review.