Add Email Validation Action

[Cedric-Magnan]

Is your feature request related to a problem? Please describe.
I have setup automated tests of the data that I receive from the manual ingestion from my client. They do not use Slack (unfortunately) or any other tool that I could use for notifications available in Great Expectations.
They have emails and mailing lists though, as well as a SMTP server that I can use. Thus, I could theoretically send emails at the end of the validation of the files I receive so they can be noticed of any issue in the ingested files.

Describe the solution you'd like
An email notification that would work just like the Slack notification but that sends emails instead.

Describe alternatives you've considered
I have setup everything in a custom module that I currently use, but I think this feature could be directly added to great_expectations.

Additional context
The email notification could look something like this (a custom renderer may also be used to enhance the email visuals) :