Note that the `sitemap:refresh` task only pings search engines at the
end, so it only does so for the `Sitemap.default_host` defined last. So
we're using the `sitemap:refresh:no_ping` task instead and pinging
search engines after creating each sitemap.
Note we're pinging search engines in staging and preproduction
environments. I'm leaving it that way because that's what we've done
until now, but I wonder whether we should only do so on production.
Since we're creating a new method to get the current url_options, we're
also using it in the dev_seeds.
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