When a node enters recovery after being in raft topology mode, topology
operations switch back to legacy mode. We want CDC to keep working when
that happens, so we need for the legacy code to be able to access
generations created back in raft mode - so that the node can still
properly serve writes to CDC log tables.
In order to make this possible, modify the legacy logic to also look for
a cdc generation in raft tables, if it is not found in legacy tables.
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