roachtest/cdc/mixed-versions: add more randomization

[jayshrivastava]

As a follow up to #107451, we should add more randomized testing during the upgrades.

See #108802 (comment)

ex.

• picking the resolved duration randomly across a set of options;
• setting different changefeed options when creating it;
• different parameters to the bank workload (number of rows, payload size, etc)
• different workloads

Jira issue: CRDB-30712

Epic CRDB-9179

[blathers-crl]

cc @cockroachdb/cdc