Add fluentbit.affinity configuration

[wigust]

What this PR does / why we need it:

Allows to configure fluentbit pods affinity, which is useful for adding a rule to not to schedule a pod on a node based on a label.

values.yaml example:

fluentbit:
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
        - matchExpressions:
          - key: node-role.kubernetes.io/edge
            operator: DoesNotExist
          - key: fluentbit.cluster.local/schedulable
            operator: NotIn
            values:
            - "false"

Does this PR introduced a user-facing change?

None

[benjaminhuo]

@wigust Thanks!