A real overseer feature (#1892)

* A real overseer feature

* Fix build without feature

* Update node/service/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
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