Rate-limit clicking on forgot my password button

[ffont]

As reported by a user:

so i found out the hard way you guys have no "email has been sent" confirmation or even blocker to stop clicking it more times on your "forgot my password" thingy, so when you put and email in you can just click infinitely

We should disable the button on click like we do for other forms.

[gauripod]

hi. could i help with this issue/bug? i'd love to take it on.