Implement bgp.originate for IPv4 and IPv6

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The initial bgp.originate attribute was added to netlab before I added IPv6 support. It's time to make it dual-stack. While we can already do that with the bgp.originate plugin, it makes no sense not to make that core functionality and add support for prefix and pool attributes (similar to static routes and prefix lists)

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Migration strategy:

• Implement Use static routes for BGP prefix origination where available #3208 and test it (for IPv4 only). At that point, the only devices still using bgp.originate in the templates would be the devices with BGP support but without support for static discard routing: cumulus, nxos, openbsd, routeros7, sonic, srlinux, srsim. I don't see any problem adding that functionality to srlinux, sros, and nxos. I'm sure @remilocherer will add that for OpenBSD.
• Change the bgp.originate attribute to have the same data type as bgp.advertise attribute (accepting IPv6)
• Add 'legacy_bgp_originate' function that would check whether the bgp.originate list is still present (wouldn't be for devices with discard routes), check whether there are any IPv6 prefixes in it and generate an error saying "use bgp.originate plugin", otherwise generate a list of IPv4 prefixes as strings (to be used in old templates)
• Mark the bgp.originate plugin as obsolete and explain it's only to be used with devices that do not support the new bgp.originate attribute