Detect `+` when validating emails for registration

[rebecca shoptaw]

Dependency to epic #7694. Subtask of #2055.

Problem

Me and @cdrini noticed when testing #9245 that the Internet Archive is no longer allowing alias emails with plus signs, i.e. "[e-mail]", to create accounts, which means we should adjust our email checks in realtime_account_validation.js and forms.py to check for this as well.

Evidence / Screenshot

Relevant URL(s)

Reproducing the bug

1. Go to /account/create on testing, staging or production
2. Try to make an account using an email with a + sign (ideally with the plus added to an existing IA or OL email, i.e. [e-mail])

• Expected behavior: Realtime error appears to indicate plus sign is not permitted
• Actual behavior: No error, account creation silently fails

Context

• Browser (Chrome, Safari, Firefox, etc):
• OS (Windows, Mac, etc):
• Logged in (Y/N): N
• Environment (prod, dev, local): all

Notes from this Issue's Lead

Proposal & constraints

1. Modify the email regex in forms.py
2. Add the email regex validator to the Email input in forms.py
3. Modify the email regex in account.py

Related files

Stakeholders

@cdrini

Note: Before making a new branch or updating an existing one, please ensure your branch is up to date.

[rebecca shoptaw]

Turns out we can fix this on the IA side instead! Handing over to them to update the endpoint so it throws an "already registered" error if the + alias matches an existing account.