[Enhancement] BGP originate does not allow 0.0.0.0/0 prefix

[jbemmel]

Context: https://netlab.tools/module/bgp/#module-bgp-originate

A topology from https://theworldsgonemad.net/2025/lab-as-code-pt2/#topology uses:

ISP:
    module: [ bgp ]
    provider: libvirt
    device: csr
    bgp.originate: 0.0.0.0/0

On the dev branch we get:

[ERRORS]  Errors found in topology.yml
[VALUE]   bgp: attribute 'nodes.ISP.bgp.originate[1]' must be IPv4 prefix outside of reserved ranges
          (0.0.0.0/0 is in local range)

In the current code base, the preferred way would be to use the bgp.session plugin and set bgp.default_originate: true

It would be nice if the (arguably) more intuitive bgp.originate: 0.0.0.0/0 would work too, or at least provide a specific error message with a recommended resolution

[ipspace]

FWIW, the root cause is #2229

I encountered the exact same problem when cleaning up the BGP labs and decided to go with bgp.default_originate, but I agree we need a more nuanced check of valid prefixes and the ability to specify which checks to apply in the attribute definition