Use custom email template for reset password feature

### Description

Current template for reset password functionality is
```

You're receiving this email because you requested a password reset for your user account at EvalAI.

Please go to the following page and choose a new password:

https://eval.ai/auth/api/password/reset/confirm/NDIzNw/5le-ad1616b4c5337004172d

Your username, in case you've forgotten: ram81

Thanks for using our site!

The EvalAI team
```

We should add a custom email template for reset password. A sample template is available [here](https://github.com/Cloud-CV/EvalAI/blob/master/apps/accounts/templates/account/email/password_reset_key_message.txt).

Refer the tutorial for an example: https://simpleisbetterthancomplex.com/tutorial/2016/09/19/how-to-create-password-reset-view.html