`bench pallet`: only require `Hash` instead of `Block` (#3244)

Preparation for https://github.com/paritytech/polkadot-sdk/issues/2664

Changes:
- Only require `Hash` instead of `Block` for the benchmarking
- Refactor DB types to do the same

## Integration

This breaking change can easily be integrated into your node via:  
```patch
- cmd.run::<Block, ()>(config)
+ cmd.run::<HashingFor<Block>, ()>(config)
```

Status: waiting for CI checks

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: cheme <emericchevalier.pro@gmail.com>