coreos-download: add routing under /coreos/download
Adds three routes under /coreos/download:
- /coreos/download/cloud_launchable/
- /coreos/download/metal_virtualized/
- /coreos/download/cloud_operators/
All of the three subroutes render with /coreos/download/index.html
but preserves the url. The frontend will then render with different
tab view according to the requested url.
This change makes sharing fedora coreos download page more convenient
by going to the target platform tab directly instead of additional
clicks.
Closes: https://github.com/coreos/fedora-coreos-tracker/issues/417
https://pagure.io/fedora-web/websites/issue/98
Signed-off-by: Allen Bai <abai@redhat.com>