doc/rados/configuration: Small improvements in ceph-conf.rst

doc/rados/configuration: Small improvements in ceph-conf.rst

Fix a missing space typo.

Use title case in section titles.

Use ref for hyperlink to a section that already has a label instead of
linking to title text of the section.

Use privileged command prompt for all ceph commands except ceph commands
that invoke help.

Use INI preformatted block for last remaining block that was just using
plain preformatted.

Signed-off-by: Ville Ojamo <14869000+bluikko@users.noreply.github.com>