api: open up /cluster/options call over injecting info into /version

api: open up /cluster/options call over injecting info into /version

To avoid returning unrelated information in the /version api call in
the future use the API endpoint that'd return the relevant
information basically anyway.

It contains most ui relevant options, like the console preference and
tag-style so allow these for users without 'Sys.Audit' on '/', for
others its unchanged, they still get the whole datacenter config.

We also add the list of allowed tags, while not strictly a datacenter
config, it's derived from the current users privileges and the
datacenter config.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>