Reduce AWS E2E Costs - windows sizing etc

At the moment the E2E tests use the same size for the windows VM as the ST2 instance (i.e. c4.large/c5.large). Update so that the windows instance size is controlled separately, as probably a micro instance is sufficient.

Update the schedule so that unstable runs are not run every day - suggest twice a week.

Move the unstable runs to Rocky from RHEL.