fix: add additional startsWith('@') check when validating domain

[karrui]

Problem

This PR adds an additional check for the allowed domains entered by the user to enforce starting with an '@' symbol. This prevents a form admin from adding a complete email address such as test@example.com into the allowed domain field.

Related to https://github.com/datagovsg/formsg-private/issues/53

Solution

Bug Fixes:

• fix: add additional startsWith('@') check when validating domain

Before & After Screenshots

BEFORE:
Allows full email domains

AFTER:
Prevents full email addresses

[liangyuanruo]

write a script to check whether the current database state is consistent with this change. otherwise, some admins may not be able to save their form.

[karrui]

write a script to check whether the current database state is consistent with this change. otherwise, some admins may not be able to save their form.

I've done a check, as of this instance the only malformed emails are testing domains by me and @syan-syan

[tshuli]

lgtm!

[mantariksh]

suggesting changing the error copy to "You may have duplicate or invalid email domains. Please check that all the domains start with @."

[liangyuanruo]

Ok