Split off from #41412

WITH HOLD support allows keeping a cursor open for longer than a transaction by writing its results into a buffer.

postgres docs on declare.

Unless WITH HOLD is specified, the cursor created by this command can only be used within the current transaction. Thus, DECLARE without WITH HOLD is useless outside a transaction block: the cursor would survive only to the completion of the statement. Therefore PostgreSQL reports an error if such a command is used outside a transaction block. Use BEGIN and COMMIT (or ROLLBACK) to define a transaction block.

If WITH HOLD is specified and the transaction that created the cursor successfully commits, the cursor can continue to be accessed by subsequent transactions in the same session. (But if the creating transaction is aborted, the cursor is removed.) A cursor created with WITH HOLD is closed when an explicit CLOSE command is issued on it, or the session ends. In the current implementation, the rows represented by a held cursor are copied into a temporary file or memory area so that they remain available for subsequent transactions.

WITH HOLD may not be specified when the query includes FOR UPDATE or FOR SHARE.

Epic CRDB-11397

Jira issue: CRDB-13412