[feature]: `ForwardingHistory`: remove default `start_time` value

[ZZiigguurraatt]

In ForwardingHistory we have a start_time that defaults to 24 hours.

We also have a max_events that defaults to 100

I'd like to argue to remove the default start_time of 24 hours since we already limit the max_events to 100. Instead, we should process all history if the value is omitted.

For new users of this command and new node runners, they may not have any forwards in the last 24 hours, but could have a small number of forwards in the last month that is even less than 100, but they won't get any results if they don't properly specify start_time. It's especially easy to miss and confuse the defaults for some of the options because of lightninglabs/lightning-api-ng#33 .