Test hybrid etcd version clusters in robustness tests

[serathius]

What would you like to be added?

E2e tests allow running clusters with different versions. With some probability (let's say 10%) we could start etcd cluster with older members.

Note; 10% would be the probability that we will run continuously in CI. Before sending a PR please run those configuration couple of hundreds times to ensure it will not cause flakes that would not be found early due to lower probability of this scenario

Why is this needed?

This should give us more trust into correctness during upgrades and downgrades

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed after 21 days if no further activity occurs. Thank you for your contributions.

[serathius]

cc @siyuanfoundation

[siyuanfoundation]

cc @henrybear327