Add resource requests to ROKS metrics pods

[csrwng]

The resources needed by these pods are very small. In practice, I haven't seen them go over 0.5m for cpu and 30Mi for memory. Not sure that it's worth parameterizing.
Fixes #85

[csrwng]

@rtheis ptal

[rtheis]

/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: csrwng, rtheis

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[rtheis]

Here's the CPU and memory usage from a ROKS 4.5 cluster just deployed. We may be able to lower these depending on long term resource utilization. But for now, the PR seems reasonable.

$ kubectl top pods -n openshift-roks-metrics
NAME                      CPU(cores)   MEMORY(bytes)   
metrics-d75db69d9-8xf5q   0m           23Mi  

[csrwng]

/cherry-pick release-4.5

[openshift-cherrypick-robot]

@csrwng: new pull request created: #87

In response to this:

/cherry-pick release-4.5

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