feat: add an API to run tasks outside of transactions

[cstockton]

This also includes an example of using it inside of mail.go

[coveralls]

Pull Request Test Coverage Report for Build 15146315184

Details

• 121 of 141 (85.82%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 70.15%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/api/mail.go	19	29	65.52%
internal/api/taskafter/taskafter.go	99	109	90.83%

Totals
Change from base Build 15141341085:	0.1%
Covered Lines:	11231
Relevant Lines:	16010

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💛 - Coveralls

[cstockton]

Some issues with this approach:

• Wrapping the json response sending is very ugly and hard to prove correct
• Invalid emails will still get signed up unless we call the validation code in mailer during tx
• Likely want to be 100% async with some retries for mail sending for this change to work