opt: add optsteps or something like it to statement bundle

Lifting complicated customer queries out of the statement bundle env to the opt_tester env is hard and some things aren't supported (materialized views). But we frequently have to do this to gain an understanding of what plans were considered and discarded and what was driving the cost tradeoffs.

Ideally we would be able to get list of all exploration steps and decisions are statement bundle create time and then also generate this from the statement bundle and diff them. This might help us to understand where/why we sometimes pick a different plan in the prod env than we do using explain from statement bundle recreate env.

Jira issue: CRDB-26024