feat: add mail header support via `GOTRUE_SMTP_HEADERS` with `$messageType`

[hf]

Adds support for additional and configurable email message headers. Set the GOTRUE_SMTP_HEADERS value to a JSON object of the shape (TypeScript notation)

{ [header: string]: string[] }

Use the special string $messageType in the value portion to identify the message type being sent (for now: invite, confirm, reauthenticate, email_change, recovery, magiclink, other).

To use this with AWS SES Feedback-ID one way to do it would be to set SES SMTP message tags:

GOTRUE_SMTP_HEADERS={"x-ses-message-tags": ["ses:feedback-id-a=<project-ref>,ses:feedback-id-b=$messageType"]}

[coveralls]

Pull Request Test Coverage Report for Build 11332733424

Details

• 44 of 55 (80.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.07%) to 57.225%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/conf/configuration.go	16	18	88.89%
internal/mailer/template.go	27	30	90.0%
internal/mailer/mailme.go	0	6	0.0%
<!--	Total:	44	55	80.0%	-->

Totals
Change from base Build 11327229130:	0.07%
Covered Lines:	9544
Relevant Lines:	16678

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💛 - Coveralls