MNTOR-1800: Part 3 - unsub emails endpoint and generate link util function

[mansaj]

References:

Jira: MNTOR-1800

Description

• Util function to generate unsubscribe URL
• API endpoint to verify unsub url and unsub the user from monthly monitor reports

How to test

• Use the function generateUnsubscribeLink to generate a link
• Try visit the url (GET request) and the user should be unsubscribed to the monitor report

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.
• If this PR implements a feature flag or experimentation, the Ship Behind Feature Flag status in Jira has been set
• 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.

[github-actions]

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[github-actions]

Cleanup completed - database 'blurts-server-pr-4973' destroyed, cloud run service 'blurts-server-pr-4973' destroyed