During forwarding of CQL EXECUTE requests, the target node may
not have the prepared statement in its cache. If we do have this
statement as a coordinator, instead of returning PREPARED NOT FOUND
to the client, we want to prepare the statement ourselves on target
node.
For that, we add a new FORWARD_CQL_PREPARE RPC. We use the new RPC
after gettting the prepared_not_found status during forwarding. When
we try to forward a request, we always have the query string (we
decide whether to forward based on this query), so we can always use
the new RPC when getting the prepared_not_found status.
After receiving the response, we try forwarding the EXECUTE request
again.
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