Enable running prometheus on arm architectures

[Pokom]

It would be useful to be able to target the specific architecture that prometheus will run on. I'm particularly interested in being able to target arm64, but this should be configurable. Here's the GKE guides on how to target different architectures.

My thought would be to expose a mixin withTolerations(arch) that would look like the following:

  withTolerations(arch)::
          prometheus_statefulset+:
            k.apps.v1.statefulSet.mixin.spec.template.spec.withTolerationsMixin(
              k.core.v1.toleration.withKey('kubernetes.io/arch') +
              k.core.v1.toleration.withOperator('Equal') +
              k.core.v1.toleration.withValue(arch) +
              k.core.v1.toleration.withEffect('NoSchedule')
            ),