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.
This includes changing the URL to #settings/preferences, with a
transparent redirect so that existing links, like the one from Welcome
Bot, continue to work.
Creates new help article for supported web browsers. Also updates
links in the `/apps` landing page as well as the unsupported-browser
template and the `set-up-your-account` article.
Fixes#14732.
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.