rgw: handle http options CORS with v2 auth

rgw: handle http options CORS with v2 auth

If we get a HTTP OPTIONS request for a presigned URL that
contains credentials we need to compute the signature
using the method given in the access-control-request-method
http header.

This is the same as performed for v4 auth in [1].

[1] https://github.com/ceph/ceph/pull/52673

Signed-off-by: Tobias Urdin <tobias.urdin@binero.com>