Add optional password reset failure emails

This change allows Open edX operators to enable password reset
failure email notifications. This is mainly useful for
explicitly informing users that there's no account associated
with their email, so that users can be sure that there wasn't
a problem with the email system.

OSPR-1832

lms/envs/common.py

@@ -418,6 +418,10 @@ FEATURES = {
 
     # Whether HTML XBlocks/XModules return HTML content with the Course Blocks API student_view_data
     'ENABLE_HTML_XBLOCK_STUDENT_VIEW_DATA': False,
+
+    # Whether to send an email for failed password reset attempts or not. This is mainly useful for notifying users
+    # that they don't have an account associated with email addresses they believe they've registered with.
+    'ENABLE_PASSWORD_RESET_FAILURE_EMAIL': False,
 }
 
 # Settings for the course reviews tool template and identification key, set either to None to disable course reviews