The metadata service docs were hard to find since they were nested
down in some nova-network admin guide docs, and they were a mix of
end user and admin deployment guide information.
This change splits out the end-user facing content into a user
guide and leaves the deployment-specific information in the admin
guide, and links are updated appropriately.
The admin guide portion also referenced some config options that no
longer exist, so those are also removed and vendordata_providers
is added with a link to the vendordata guide. The options themselves
are cleaned up for their current groups and linked to the config option
docs.
Change-Id: I66035366f3a7ca62ea12d6afa74d13db01ec9f8d
43f91a87cb