QUIC-LB should rotate established CIDs when the configuration is rotated

According to https://github.com/quicwg/load-balancers/blob/7ba71c035a4a57b722281dd88fa0b4ca04f2bfe5/draft-ietf-quic-load-balancers.md?plain=1#L197-L199:

> Servers MUST use that QUIC
version's methods to update the client with CIDs (e.g., NEW_CONNECTION_ID
frames) using the new configuration and retire CIDs using the old configuration.

Envoy is not currently doing this when the configuration is rotated.

This should probably be done over a medium period of time, in the same way that connection draining is, because updating a large number of established connections is resource intensive.