router ID generation must be addressed in case of IPv6

[zolug]

Is your feature request related to a problem? Please describe.
Consider IPv6 only cluster where Attractor relies on network-attachment-definition to provide interface for cluster breakout:
The NAD takes care of IP address allocation through some IPAM of choice to assign IPv6 address only. Howver, due to lack of any feasible IPv4 addresses, BIRD in LB-FE will bail out with following error: "Cannot determine router ID, please configure it manually"
Thus, FE containers get stuck in CrashLoopBackOff.

That's because the configuration generated for BIRD does not contain a router ID. Having unique router IDs would require some IPAM like feature that would assign router IDs to FE instances.
The difference compared to VLAN-NSE configuration is that in case of NSM provided external interface, IPv4 addresses were always assigned by default.

As a workaround, the IPAM config part in the NAD could still assign an IPv4 address that could be used by BIRD as router ID.

Describe the solution you'd like
Consider if router ID should be provided independently from the external interface's configuration.

Describe alternatives you've considered
Some time ago a tested with a router ID shared among the FEs of the same Attractor. The peers routers also running BIRD seemed to have no problem with that. Although I haven't done extensive testing.

Additional context
N/A