implement dispute participation subsystem (#3234)

* implement dispute participation subsystem

* guide: minor fix in dispute participation

* Update node/core/dispute-participation/src/lib.rs

Co-authored-by: Andronik Ordian <[email protected]>

* dispute: add comments to participation logic

* dispute-coordinator: fix test compilation

* implementers-guide: update dispute participation

* dispute-participation: add error for missing validation code

* dispute-participation: add tests

* Update node/core/dispute-participation/src/lib.rs

Co-authored-by: Robert Habermeier <[email protected]>

* guide: update overseer protocol dispute participation message

* dispute-participation: remove duplication in tests

Co-authored-by: Andronik Ordian <[email protected]>
Co-authored-by: Robert Habermeier <[email protected]>