Allow external kml and geojson files from an allowlist of hosts

Since 15.0.0 the kml and geojson parameters load only files that are on the wiki, unless $egMapsAllowExternalDataFiles is set to true, which allows any URL again. Wikis that depend on one or two trusted sources, such as an open-data portal or their own file server, have no middle ground: they either lose those maps or accept every host.

Proposal

A setting that lists the hosts external data files may come from, for example:

$egMapsAllowedDataFileHosts = [ 'data.example.org', '*.geo.example.net' ];

• A URL in kml or geojson loads if $egMapsAllowExternalDataFiles is true, as now, or if its host matches the list. The default is an empty list, so nothing changes for existing wikis.
• Entries are host names, and a leading *. covers subdomains.
• The list applies to both paths: KML fetched by the viewer's browser and GeoJSON fetched by the server. The existing server-side safeguards, blocked private address ranges and pinned DNS, stay in force for listed hosts, and a redirect to a host outside the list is not followed.
• NetworkLink elements inside a KML document follow the same list.
• MediaWiki:Maps gets a counterpart, general.allowedDataFileHosts, like the other settings.

MediaWiki core has the same pattern in $wgCopyUploadsDomains for upload by URL, whose matching rules could be reused.

Trace how kml and geojson URLs are handled in both the viewer's browser path and the server-side GeoJSON path, then compare host matching with MediaWiki's $wgCopyUploadsDomains rules. Verify the empty-list default, wildcard subdomains, redirects, KML NetworkLink handling, and existing private-address and pinned-DNS safeguards for both configuration settings.