Docs for beforeHistorySave event

[limugob]

https://github.com/bigskysoftware/htmx/blob/f4f448db0a413e403d3c7f627d9e6d2b356bf0d8/www/content/events.md?plain=1#L265-L268

The description of the beforeHistorySave and the historyRestore event is the same, but beforeHistorySave should have something like:

This event is triggered before the content is saved in the history api.

https://github.com/bigskysoftware/htmx/blob/f4f448db0a413e403d3c7f627d9e6d2b356bf0d8/www/content/events.md?plain=1#L257-L260