Added support for Affinity and Tolerations

[Dan0x54]

This will add support for tolerations and affinity as requested in #242.

[benjaminjb]

This seems reasonable to me, though I tend to prefer the if ... end style of dropping fields if blank. What do you think of making that change?

I'm also wary of having our kustomize and Helm installations drift too far apart, but let me talk it out for a moment if we make this change:

• If I'm a Helm chart user who wants affinity on my PGO installation, I would add values to an installation (either through the command line or by downloading the chart and making the changes -- basically, through changing the values.yaml)
• If I'm a kustomize user who wants affinity, I download the kustomize files and change the manager.yaml file directly (or maybe add an overlay/patch to the kustomization.yaml)

Which is the same way we handle, say, resources. OK, I've talked myself into this being a Helm-only change.