api: nodes: allow usage of query url metadata with Sys.AccessNetwork

api: nodes: allow usage of query url metadata with Sys.AccessNetwork

This was restricted to Sys.Modify + Sys.Audit on the whole cluster to
ensure that only trusted users get access to a method that can scan
the (local) network from the POV of the Proxmox VE node, even if only
through HTTP HEAD requests.

Nowadays there's enough user interest [0] to warrant a separate access
privilege to cover such an use case, and while most of the requests
are for the download-url storage API endpoint, this method here is not
only a bit less powerful than the storage one, it's rather tied to the
latter anyway (e.g. for querying the metadata of a URL in the web UI
for name and size before downloading it to a storage).

For backwards compatibility keep the old check and add the new
privilege as alternative to fulfill the permission requirements of
that API endpoint.

[0]: https://bugzilla.proxmox.com/show_bug.cgi?id=5254

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Tested-by: Hannes Duerr <h.duerr@proxmox.com>
Reviewed-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>