Fix the pods limits according to best practice

[vladimirhasko]

The applied limits changes at #936
are causing that limits and requests are on the same value.
This endangers pod to out of memory situation when it needs some RAM (requests) but it's not allowed to use more (equal to limits)
Therefore raise limits to be higher than requests
Additionally these changes should be applied in overalay approach instead of base changes.

[gtema]

Well, actually only limits should have been raised and requests not touched. requests influences where K8 will schedule the pod (ensure that at least that amount is available) - and with previous values Zuul was working perfectly fine for a very long time. Fact that under some conditions it may require more is controlled by limits which define the upper limit of what pod can consume