doc/man/8/ceph-volume: specify "program" for subcommands

doc/man/8/ceph-volume: specify "program" for subcommands

as per
https://www.sphinx-doc.org/en/master/usage/restructuredtext/domains.html

> Like py:currentmodule, this directive produces no output. Instead, it
> serves to notify Sphinx that all following option directives document
> options for the program called name.
> ...
> The program name may contain spaces (in case you want to document
> subcommands like svn add and svn commit separately).

and to avoid the warnings like:

doc/man/8/ceph-volume.rst:424: WARNING: Duplicate explicit target name:
"cmdoption-ceph-volume-h".

we should specify different "program" for different set of options.

Signed-off-by: Kefu Chai <kchai@redhat.com>