rgw: allow specifying ssl certificate for radosgw-admin operations

rgw: allow specifying ssl certificate for radosgw-admin operations

for example

../src/mrun c2 radosgw-admin realm pull --url=https://localhost:1443 --access-key a2345678901234567890 --secret a234567890123456789012345678901234567890 --default --rgw_verify_ssl_cacert=./cert.pem

../src/mrun c2 radosgw-admin period pull --url=https://localhost:1443 --access-key a2345678901234567890 --secret a234567890123456789012345678901234567890 --default --rgw_verify_ssl_cacert=./cert.pem

../src/mrun c2 radosgw-admin period update --commit --rgw_verify_ssl_cacert=./cert.pem

../src/mrun c2 radosgw-admin sync status --rgw_verify_ssl_cacert=./cert.pem

fixes: https://tracker.ceph.com/issues/53588

Signed-off-by: Mark Kogan <mkogan@redhat.com>