pveceph: Reorganize TOC for new sections

pveceph: Reorganize TOC for new sections

Put the previous added sections into subsection for a better outline of
the TOC.

With the rearrangement of the first level titles to second level, the
general descriptions of a service needs to move into the new first level
titles. And add/corrects some statements of those descriptions.

Signed-off-by: Alwin Antreich <a.antreich@proxmox.com>