doc/dev: use http://docs.ceph.com/en/latest/ instead of /docs/master/ for docs

doc/dev: use http://docs.ceph.com/en/latest/ instead of /docs/master/ for docs

Several links under http://docs.ceph.com/docs/master/ were unable to access.
Change them to http://docs.ceph.com/en/lastest so we can access them directly.

Signed-off-by: haoyixing <haoyixing@kuaishou.com>