The ROOT_DOMAIN_LANDING_PAGE boolean setting is set based on
whether the root domain is a landing page or can host a realm.
We set it to False by default as we don't expect it to be used
by someone outside zulip.com (mentioned in 3173db37f7).
But the development environment uses the root domain 'zulipdev.com'
as landing page and the default realm is hosted at the subdomain
'zulip.zulipdev.com'.
So, this commit overrides the default value in 'dev_settings.py'.
Earlier, the zulip.com equivalent landing pages, including the
help center pages were not accessible in the dev environment.
This commit fixes those bugs.
Fixes#30750.
1e7468bbe5