The Antithesis config image was not being uploaded during CI runs, only
the workload image. This caused experiment failures when the config
image expired from the registry after 6 months of inactivity.
This adds a "limbo_stress" tool for stress testing Limbo in
non-deterministic way together with support code to run the tests under
Antithesis (which makes them deterministic). The stress tester does not
really do anything useful yet, this is just a step to make sure we can
run tests under Antithesis.
