Expose a friendly way to run the "TOUCH" command

We currently run the [`TOUCH`](https://redis.io/commands/touch) command like this:
```csharp
byte[] keyToTouch = /* ... */;
object[] args = { keyToTouch };
db.Execute("TOUCH", args, CommandFlags.FireAndForget);
```

It would be nice to have a friendlier version of this.