[WIP]Support nested BGP peering with calico-nodes running in local kubevirt VM pods

[song-jiang]

Description

This PR adds support for allowing calico-node to peer with calico-node instances running inside KubeVirt VM pods locally, based on the labels of the VM pods.

API changes:

• New field LocalWorkloadSelector to BGPPeer resource.
• New field localWorkloadPeeringIPV4 and localWorkloadPeeringIPV4 to BGPConfigurations.

Felix changes:

• It watches BGPPeer and calculates local workloads selected by the BGPPeer.
• It populates endpoint status files with peering information.
• It add localWorkloadPeeringIP to the network interface of the workload selected by the BGPPeer.

Confd changes

• It watches endpoint status files updated by Felix.
• It reconfigures bird.cfg/bird6.cfg based on the peering information read from endpoint status files.

libcalico-go changes

• Added status-file-writer and status-file-watcher.

Related issues/PRs

Todos

• Tests
• Documentation
• Release note

Release Note

TBD

Reminder for the reviewer

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[aaaaaaaalex]

Couldn't spot any glaring issues (though I understand you know of one!)