EPM and staking events improvement (#13035)

* EPM and staking events improvement

* Uses RawOrigin in ElectionCompute event

* Refactors new phase events to PhaseTransition event

* PhaseTransitioned and remove RawOrigin from event

* Adds helpers for epm phase transition and staking force new

* addresses review comments

* nit: removes unecessary clone

* fixes benchmarks

Co-authored-by: parity-processbot <>