Email: Allow users to control partial send or send all behavior

[dospromptman]

Currently, if there are any errors while sending a list of emails using the send emails action, then some emails are still sent while the emails with errors are not sent.

We should allow the user to control this behavior when sending emails using the send emails action. They should be able to choose whether partial send should be allowed or if no emails should be sent in the case of any errors. This may make it easier for them to recover from errors without a lot of manual follow up work (i.e. manual resend of emails to recipients that errored the first time).