Update to maintain consistency with the value of the context property
used in the other docs.
We avoid using the context property for these instances because we
always want them to show "your-org.zulipchat.com" irrespective of the
domain the docs are hosted in. Hence, the manual replacements.
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.
