ceph-dashboard: fix oject gateway integration

ceph-dashboard: fix oject gateway integration

Since [1] multiple ceph dashboard commands have been removed and this is
breaking the current ceph-ansible dashboard with RGW automation.
This removes the following dashboard rgw commands:

- ceph dashboard set-rgw-api-access-key
- ceph dashboard set-rgw-api-secret-key
- ceph dashboard set-rgw-api-host
- ceph dashboard set-rgw-api-port
- ceph dashboard set-rgw-api-scheme

Which are replaced by `ceph dashboard set-rgw-credentials`

The RGW user creation task is also removed.

Finally moving the delegate_to statement from the rgw tasks at the block
level.

[1] https://github.com/ceph/ceph/pull/42252

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit 2ee2194ee0aff2e9d2f185e46366f879b9def1ab)