Email action support

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I'd raise a PR to flesh out the current partial implementation if I could figure out how to do it...

We use email actions on a handful of detections to initiate callouts (don't ask, I'm not a fan but it's the norm in my org) and it would be awesome if we were able to configure these in our content pack.

Field support for our use case doesn't need to be extensive, just the to, subject and message fields are sufficient, though it would be a bonus if some of the attachment, inline results, or results link options were available.

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Attempting to implement this in #397