roachtest/cdc/mixed-versions: add more randomization

As a follow up to https://github.com/cockroachdb/cockroach/issues/107451, we should add more randomized testing during the upgrades.

See https://github.com/cockroachdb/cockroach/pull/108802#issuecomment-1681249056

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