Test validator disabling on Westend

[tdimitrov]

Disabling is triggered by staking pallet which is not added to Rococo Westend. Test if/how validator disabling will work there.

[Overkillus]

Needs to be tested in Westend as Rococo doesn't use the staking pallet which is crucial for processing offences and adding validators to the disabled list.

[tdimitrov]

It was tested with zombienet with westend-local and malus nodes. Testing it on the actual network won't bring additional benefit.