[11.x] Trigger event on password reset link send

[Muffinman]

This PR adds are new event called PasswordResetLinkSent, which is triggered by the PasswordBroker directly after the Notification is queued.

We had a need for this ourselves, and this seemed to be the only missing event in the auth / reset chain, and seems like something that may be useful for others.

Note that it's possible to trigger your own event within the application layer at least a couple of different ways, using middleware or within a Notification event listener, but those solutions seem messy comparatively.

When looking at the other Auth related events already supported I think doing this natively makes sense.

Note: I decided not to trigger the event if $callback is passed in, since we will not know how this is handled within the callback.

[Muffinman]

Meant to submit this as Draft, will resubmit after tests are passing.

[taylorotwell]

We can't call the global event helper from this the Illuminate\Auth package.

[Muffinman]

@taylorotwell to be clear, are you saying this is an impossible problem to solve within the Auth package?

Or would you accept a PR to add helpers to the Illuminate/Auth package composer.json or otherwise conditionally call the event when the presence of event helper is detected?

[Muffinman]

I think I could have another go at this, adding setDispatcher methods as per the StatefulGuard class, but I think that will end up being a much bigger PR and I don't hold out much hope of it being accepted.