Allow "send me an email" in personal rules to punch through settings

Summary:
Fixes T7731. When a user writes a "Send me an email" rule, always try send them an email, even if their notification settings would normally downgrade it to a notification.

In particular, this is stronger than these downgrades:

• Downgrades due to "self actions";
• downgrades due to "mail tags".

Test Plan:

• Wrote various Herald rules with "Send me an email" rules.
• Used bin/mail list-outbound / show-outbound to vet generated mail.
• Mail reacted properly to a variety of conditions (disabled accounts, settings, "send me an email" rule, forced delivery).

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7731

Differential Revision: https://secure.phabricator.com/D12300