"SELECT FOR UPDATE" queries incompatable with CRDB v19 and lower

[ruteben]

I was running the TPCC benchmark on CRDB v2.1.9 and ran into an issue with two NewOrder queries using "SELECT FOR UPDATE", which CockroachDB only supports since version 20.1 (released May this year). Besides TPCC's NewOrder, this kind of query is also used in YCSB's ReadModifyWrite.

I'm aware that this project provides the necessary docker files to run the latest version of CockroachDB, but it is sometimes preferred to use older versions for the sake of stability or comparison.

Do you intend to support version v19 and older? If you do, an alternate query that does not use the "SELECT FOR UPDATE" would be required for the older versions. If you don't, then it might be a good idea to include the required minimum version in the readme.