Simplify keybinding registration

Guido Güntherrequested to merge
guidog/phosh:keybindings into main

Getting allocations right for the actions and the bindings name is error prone so lets have a macro that simplifies this.

I'll introduce the macro in !1775 (merged) too but figured moving the other code over might be simpler in a separate MR to not munge too many things together.

/cc @arun-mani-j

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