Add email as an Integration

[unkrich]

Description

Currently we support alerts via webhook and slack (webhooks). Both are relatively early, but we are looking to support email notifications as well.

Expected behavior

Expected behavior is to be able to create an email alert notification.

This would require adding an integration option on the frontend: https://github.com/monosidev/monosi/blob/master/src/ui/src/components/forms/IntegrationForm/index.tsx

As well as an integration implementation on the backend https://github.com/monosidev/monosi/tree/master/src/server/integrations

We should consider better subclassing and defining the alert that is going out to each of these integrations as well.

Additional context

Implementation likely uses https://docs.python.org/3/library/smtplib.html to send email and exposes configuration variables to define the SMTP server/auth information

[yongyx]

I would like to contribute to this issue.

[iporollo]

Thanks for offering to help here @yongyx , let us know if you have any questions!

[unkrich]

Also, our integration code is a bit of a mess today, so if you find this to be a bit more challenging than expected, this is probably because we should consider refactoring the base implementation.

Let me know if that's the case!