RFE: Allow killing stuck migration connection

Description of problem:

If a migration is terminated because of broken TCP connection it may a long time before QEMU sees connection closing. Meanwhile it may be stuck trying to send data to the other side. Upstream has a solution for this: "yank" command:

https://gitlab.com/qemu-project/qemu/-/blob/master/qapi/yank.json

We should adopt it in libvirt.

Version-Release number of selected component (if applicable):

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Additional info:

See discussion to bug 1945532.