OSM plugin still uses http only for maps-redirect.qt.io

The OSM plugin only uses the maps-redirect service via http. It should be changed to support https as well. The service enables Qt Location users find alternate sources for OSM maps content in case one service becomes unavailable. The Qt company hosts the service data on its own web servers.

This issue was flagged by Qt IT because https has become the norm these days.

Note that SSL/https support is not always enabled on all Qt builds. Also, the patch should try https first and fall back to http if it fails. Alternatively we could consider making the plugin dependent on SSL support and otherwise not build it at all.