WIP enable mw api emailuser backend

[jsnshrmn]

provides features required for mass emailing via WMF Cloud VPS.

Bug: T412427

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• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Minor change (fix a typo, add a translation tag, add section to README, etc.)