[5.7] Add line about expiring password reset in notification email

[michaeldyrynda]

I've recently started using the password resets in one of our apps at work, and the most common feedback we receive is that "it doesn't work". This is always because the link is expired.

Per suggestions from Postmark, I've added a line that pulls the expiry config value in to the notification email.

I'm not sure of the significance of using transChoice over getFromJson here, but I couldn't get the choice to work otherwise.

Happy to make changes if anybody else (ping @themsaid) has feedback on another approach; I don't want to have a line that doesn't work for those using JSON language files if the transChoice method doesn't work with that properly.

[taylorotwell]

There is probably another way to phrase it so that you could use getFromJson... Something like:

"Minutes until password reset link expires: #"

[taylorotwell]

I just used getFromJson. In theory it will read weird if the expiry is set to 1 minute but I think that's probably not going to happen in practice. Setting the expire link to 1 minute would never be a good idea in production just due to slight email delivery delays, etc.