docs: Document mail-{host,service}-notification -X option

[yhabteab]

fixes #10002

[oxzi]

Thanks, looks good to me!

I have verified that all command arguments from the two NotificationCommands are now listed here. For the future, these two documentation tables may be reordered to match the order in the NotificationCommands to ease comparing.

[yhabteab]

For the future, these two documentation tables may be reordered to match the order in the NotificationCommands to ease comparing.

I was thinking the same but also didn't want to mix required and optional arguments, i.e. first list required ones and then the optional args.