roachtest, workload: large re-write of interleaved-partition test and workload

[BramGruneir]

The interleaved partition workload and test were not performing the correct
operations and there was a good amount of leftover cruft from experiments that
were run. This commit fixes most of those problems.

A non-exhaustive selection of the updates:

• All inserts occurred in the east so everything was stored with the
  leaseholders being locked to the east dc. These should be split evenly between
  east and west and now are again.
• Both the retrieve and update operations did not run against actual session
  ids. So all of their operations where essentially noops.
• The workloads are now run from different machines to not interfere with
  cockroach.
• I greatly reduced the number of options being passed into the test. There was
  no need for most of them.
• Removed the non-partitioned index on sessions.created.
• Updated the session ids to show both the node in which they were added as
  well as the worker number. This proves we have a nice spread, as expected.

There's still some more to do here, such as put the full retrieve and update
operations inside a transaction. And try to reduce contention by adding in a
partitioned index for deletes.

All of this work was prompted by #28921, which shows that we had collisions.
Now that the workload is running correctly, if this happens again, we will have
more insight into what's going on.

Release note: None

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