Run OCW miner for staking election every once in a while on westend

[Ank4n]

The EPM pallet uses a multi-phase process to select winners from a set of validators. The first phase, called the signed phase, involves accepting a solution from an offchain staking miner. Following this is an unsigned phase in which the validator computes and submit a solution as an inherent using an offchain worker. This solution is usually of lower quality than the one computed by the staking miner and is not typically used if the chain has already received a good signed solution. However, it is important to ensure that the offchain worker can provide a valid solution when needed.

In order to verify that offchain workers are functioning correctly, we can disable the signed phase during some of the elections on our Westend testnet. This means that we will only accept solutions from offchain workers for a certain number of elections (for example, 1 out of every 4 elections).