rgw: tempurl signature fixes: support sha256 and sha512

rgw: tempurl signature fixes: support sha256 and sha512

The latest openstack swift logic supports sha256 and sha512 checksums
for tempurl and formpost, which can be either hexadecimal or
hashname:base64.  This adds logic to inspect the incoming signature
for type and to internally construct the same hash to compare.

Also:: fixes an incidental crash if a malformed swift path does not
contain an object name.

Fixes: https://tracker.ceph.com/issues/56564
Signed-off-by: Marcus Watts <mwatts@redhat.com>