feat: email address changed notification

[issuedat]

This PR adds support for sending the user an email notification when their email has been changed.

3 new environment variables are introduced:

• GOTRUE_MAILER_SUBJECTS_EMAIL_CHANGED_NOTIFICATION: Email subject to use for password changed notification.
• GOTRUE_MAILER_TEMPLATES_EMAIL_CHANGED_NOTIFICATION: The URL to specify a custom template.
• GOTRUE_MAILER_NOTIFICATIONS_EMAIL_CHANGED_ENABLED: whether the notification is enabled or not.

The feature is disabled by default. To enable it, the GOTRUE_MAILER_NOTIFICATIONS_EMAIL_CHANGED_ENABLED environment variable must be set to true.

The default email will look as follows:

[coveralls]

Pull Request Test Coverage Report for Build 18039665289

Details

• 74 of 93 (79.57%) changed or added relevant lines in 5 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.05%) to 67.686%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/api/verify.go	3	6	50.0%
internal/api/mail.go	60	66	90.91%
internal/mailer/templatemailer/templatemailer.go	0	10	0.0%

Files with Coverage Reduction	New Missed Lines	%
internal/mailer/templatemailer/templatemailer.go	6	78.99%

Totals
Change from base Build 18014087012:	0.05%
Covered Lines:	13305
Relevant Lines:	19657

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💛 - Coveralls

[cstockton]

👍