Add node selectors fields in helm chart to control scheduling of OLM and operator pods

[ddelnano]

Summary: Add node selectors fields in helm chart to control scheduling of OLM and operator pods

Previously a helm chart user could only specify the node selectors for the vizier components. This PR allows for applying node selectors to OLM and the operator. This was feedback from @ashutoshrathore after the functionality from #1887 was released.

Relevant Issues: #1861

Type of change: /kind feature

Test Plan: Tested the following scenarios

• Used helm template to verify that the manifests are the same if node selectors are not defined

$ helm template pixie-operator k8s/operator/helm/ -f k8s/operator/helm/values.yaml --debug  > new.yaml
install.go:200: [debug] Original chart version: ""
install.go:217: [debug] CHART PATH: /home/ddelnano/code/pixie-worktree/k8s/operator/helm

# Switch branches to capture templated output from existing helm chart
$ git checkout main
Switched to branch 'main'
Your branch is up to date with 'origin/main'.
$ helm template pixie-operator k8s/operator/helm/ -f k8s/operator/helm/values.yaml --debug  > old.yaml
install.go:200: [debug] Original chart version: ""
install.go:217: [debug] CHART PATH: /home/ddelnano/code/pixie-worktree/k8s/operator/helm

$ diff old.yaml new.yaml
$

• Deployed a local version of the helm chart to a cluster and verified that the node selector values are set properly for pods in the olm and px-operator namespace
• Verified that pods failed to schedule if the pinned host was terminated

$ kubectl -n olm get pods
NAME                                READY   STATUS    RESTARTS   AGE
catalog-operator-77554fbc46-zjq8m   0/1     Pending   0          2m13s
olm-operator-76dc499446-d8qvh       0/1     Pending   0          2m11s
$ kubectl -n px-operator get pods
NAME                               READY   STATUS    RESTARTS   AGE
vizier-operator-5ff9749c94-98q87   0/1     Pending   0          2m17s

Changelog Message: Add support for specifying node selector in the helm chart for OLM and operator pods