This commit adds a new section named "Notifications security"
below "Automated messages and emails" in Organization settings.
The "Allow message content in message notification emails"
setting is moved from "Automated messages and emails" section
to this new section.
This serves as a prep work as we plan to add a new setting
"Require end-to-end encryption for push notification content"
in this section.
Fixes part of #35370.
We move "Allow message content in message notification emails" setting
from "Other settings" subsection to "Automated messages and emails"
subsection.
Fixes#25339.
These files are not Jinja2 templates, so there's no reason that they needed
to be inside `templates/zerver`. Moving them to the top level reflects their
importance and also makes it feel nicer to work on editing the help center content,
without it being unnecessary buried deep in the codebase.
