Document setting the keys that will send a message or create a new
line when composting a message via the compose box and via the
personal settings overlay.
Updates links and redirect from former help center article about
this feature.
Fixes#31620.
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.
Lauryn Menard
David Rosa
Lauryn Menard