At the request of Parity's Parachains Core team, this updates the no_show_slots configuration from 2 to 3.

This increase provides more time for validators to fetch a PoV and run the parachain validation function in adverse network conditions. Increasing the no show time limit reduces the number of missed approvals and will reduce the load on the network.

Requires whitelist by https://kusama.subsquare.io/fellowship/referendum/44