Updates help center, integration and contributor docs where for
the new subsections on the organization settings tab, which were
changed in #33605.
Previously, these settings were all in the "Other settings"
subsection for that organization settings tab.
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.
