fix: case insensitive email

[mansaj]

References:

Jira: MNTOR-
Figma:

Description

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Checklist (Definition of Done)

• Localization strings (if needed) have been added.
• Commits in this PR are minimal and have descriptive commit messages.
• I've added or updated the relevant sections in readme and/or code comments
• I've added a unit test to test for potential regressions of this bug.
• Product Owner accepted the User Story (demo of functionality completed) or waived the privilege.
• All acceptance criteria are met.
• Jira ticket has been updated (if needed) to match changes made during the development process.
• Jira ticket has been updated (if needed) with suggestions for QA when this PR is deployed to stage.

[rhelmer]

Would you mind filing a followup ticket to:

1. look at the impact on the postgres stats (I suspect the index won't be as effective)
2. normalize the table if we can't adjust the index for (1)

I'm going to file one to consider moving to fxa uid instead of using primary_email as an identifier, I think it'd be a more stable identifier and email has undesirable properties like this.